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Diffstat (limited to 'Eigen/src/Core/arch/Default/GenericPacketMathFunctions.h')
| -rw-r--r-- | Eigen/src/Core/arch/Default/GenericPacketMathFunctions.h | 1649 |
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diff --git a/Eigen/src/Core/arch/Default/GenericPacketMathFunctions.h b/Eigen/src/Core/arch/Default/GenericPacketMathFunctions.h new file mode 100644 index 000000000..c9fbaf68b --- /dev/null +++ b/Eigen/src/Core/arch/Default/GenericPacketMathFunctions.h @@ -0,0 +1,1649 @@ +// This file is part of Eigen, a lightweight C++ template library +// for linear algebra. +// +// Copyright (C) 2007 Julien Pommier +// Copyright (C) 2014 Pedro Gonnet (pedro.gonnet@gmail.com) +// Copyright (C) 2009-2019 Gael Guennebaud <gael.guennebaud@inria.fr> +// +// This Source Code Form is subject to the terms of the Mozilla +// Public License v. 2.0. If a copy of the MPL was not distributed +// with this file, You can obtain one at http://mozilla.org/MPL/2.0/. + +/* The exp and log functions of this file initially come from + * Julien Pommier's sse math library: http://gruntthepeon.free.fr/ssemath/ + */ + +#ifndef EIGEN_ARCH_GENERIC_PACKET_MATH_FUNCTIONS_H +#define EIGEN_ARCH_GENERIC_PACKET_MATH_FUNCTIONS_H + +namespace Eigen { +namespace internal { + +// Creates a Scalar integer type with same bit-width. +template<typename T> struct make_integer; +template<> struct make_integer<float> { typedef numext::int32_t type; }; +template<> struct make_integer<double> { typedef numext::int64_t type; }; +template<> struct make_integer<half> { typedef numext::int16_t type; }; +template<> struct make_integer<bfloat16> { typedef numext::int16_t type; }; + +template<typename Packet> EIGEN_STRONG_INLINE EIGEN_DEVICE_FUNC +Packet pfrexp_generic_get_biased_exponent(const Packet& a) { + typedef typename unpacket_traits<Packet>::type Scalar; + typedef typename unpacket_traits<Packet>::integer_packet PacketI; + enum { mantissa_bits = numext::numeric_limits<Scalar>::digits - 1}; + return pcast<PacketI, Packet>(plogical_shift_right<mantissa_bits>(preinterpret<PacketI>(pabs(a)))); +} + +// Safely applies frexp, correctly handles denormals. +// Assumes IEEE floating point format. +template<typename Packet> EIGEN_STRONG_INLINE EIGEN_DEVICE_FUNC +Packet pfrexp_generic(const Packet& a, Packet& exponent) { + typedef typename unpacket_traits<Packet>::type Scalar; + typedef typename make_unsigned<typename make_integer<Scalar>::type>::type ScalarUI; + enum { + TotalBits = sizeof(Scalar) * CHAR_BIT, + MantissaBits = numext::numeric_limits<Scalar>::digits - 1, + ExponentBits = int(TotalBits) - int(MantissaBits) - 1 + }; + + EIGEN_CONSTEXPR ScalarUI scalar_sign_mantissa_mask = + ~(((ScalarUI(1) << int(ExponentBits)) - ScalarUI(1)) << int(MantissaBits)); // ~0x7f800000 + const Packet sign_mantissa_mask = pset1frombits<Packet>(static_cast<ScalarUI>(scalar_sign_mantissa_mask)); + const Packet half = pset1<Packet>(Scalar(0.5)); + const Packet zero = pzero(a); + const Packet normal_min = pset1<Packet>((numext::numeric_limits<Scalar>::min)()); // Minimum normal value, 2^-126 + + // To handle denormals, normalize by multiplying by 2^(int(MantissaBits)+1). + const Packet is_denormal = pcmp_lt(pabs(a), normal_min); + EIGEN_CONSTEXPR ScalarUI scalar_normalization_offset = ScalarUI(int(MantissaBits) + 1); // 24 + // The following cannot be constexpr because bfloat16(uint16_t) is not constexpr. + const Scalar scalar_normalization_factor = Scalar(ScalarUI(1) << int(scalar_normalization_offset)); // 2^24 + const Packet normalization_factor = pset1<Packet>(scalar_normalization_factor); + const Packet normalized_a = pselect(is_denormal, pmul(a, normalization_factor), a); + + // Determine exponent offset: -126 if normal, -126-24 if denormal + const Scalar scalar_exponent_offset = -Scalar((ScalarUI(1)<<(int(ExponentBits)-1)) - ScalarUI(2)); // -126 + Packet exponent_offset = pset1<Packet>(scalar_exponent_offset); + const Packet normalization_offset = pset1<Packet>(-Scalar(scalar_normalization_offset)); // -24 + exponent_offset = pselect(is_denormal, padd(exponent_offset, normalization_offset), exponent_offset); + + // Determine exponent and mantissa from normalized_a. + exponent = pfrexp_generic_get_biased_exponent(normalized_a); + // Zero, Inf and NaN return 'a' unmodified, exponent is zero + // (technically the exponent is unspecified for inf/NaN, but GCC/Clang set it to zero) + const Scalar scalar_non_finite_exponent = Scalar((ScalarUI(1) << int(ExponentBits)) - ScalarUI(1)); // 255 + const Packet non_finite_exponent = pset1<Packet>(scalar_non_finite_exponent); + const Packet is_zero_or_not_finite = por(pcmp_eq(a, zero), pcmp_eq(exponent, non_finite_exponent)); + const Packet m = pselect(is_zero_or_not_finite, a, por(pand(normalized_a, sign_mantissa_mask), half)); + exponent = pselect(is_zero_or_not_finite, zero, padd(exponent, exponent_offset)); + return m; +} + +// Safely applies ldexp, correctly handles overflows, underflows and denormals. +// Assumes IEEE floating point format. +template<typename Packet> EIGEN_STRONG_INLINE EIGEN_DEVICE_FUNC +Packet pldexp_generic(const Packet& a, const Packet& exponent) { + // We want to return a * 2^exponent, allowing for all possible integer + // exponents without overflowing or underflowing in intermediate + // computations. + // + // Since 'a' and the output can be denormal, the maximum range of 'exponent' + // to consider for a float is: + // -255-23 -> 255+23 + // Below -278 any finite float 'a' will become zero, and above +278 any + // finite float will become inf, including when 'a' is the smallest possible + // denormal. + // + // Unfortunately, 2^(278) cannot be represented using either one or two + // finite normal floats, so we must split the scale factor into at least + // three parts. It turns out to be faster to split 'exponent' into four + // factors, since [exponent>>2] is much faster to compute that [exponent/3]. + // + // Set e = min(max(exponent, -278), 278); + // b = floor(e/4); + // out = ((((a * 2^(b)) * 2^(b)) * 2^(b)) * 2^(e-3*b)) + // + // This will avoid any intermediate overflows and correctly handle 0, inf, + // NaN cases. + typedef typename unpacket_traits<Packet>::integer_packet PacketI; + typedef typename unpacket_traits<Packet>::type Scalar; + typedef typename unpacket_traits<PacketI>::type ScalarI; + enum { + TotalBits = sizeof(Scalar) * CHAR_BIT, + MantissaBits = numext::numeric_limits<Scalar>::digits - 1, + ExponentBits = int(TotalBits) - int(MantissaBits) - 1 + }; + + const Packet max_exponent = pset1<Packet>(Scalar((ScalarI(1)<<int(ExponentBits)) + ScalarI(int(MantissaBits) - 1))); // 278 + const PacketI bias = pset1<PacketI>((ScalarI(1)<<(int(ExponentBits)-1)) - ScalarI(1)); // 127 + const PacketI e = pcast<Packet, PacketI>(pmin(pmax(exponent, pnegate(max_exponent)), max_exponent)); + PacketI b = parithmetic_shift_right<2>(e); // floor(e/4); + Packet c = preinterpret<Packet>(plogical_shift_left<int(MantissaBits)>(padd(b, bias))); // 2^b + Packet out = pmul(pmul(pmul(a, c), c), c); // a * 2^(3b) + b = psub(psub(psub(e, b), b), b); // e - 3b + c = preinterpret<Packet>(plogical_shift_left<int(MantissaBits)>(padd(b, bias))); // 2^(e-3*b) + out = pmul(out, c); + return out; +} + +// Explicitly multiplies +// a * (2^e) +// clamping e to the range +// [NumTraits<Scalar>::min_exponent()-2, NumTraits<Scalar>::max_exponent()] +// +// This is approx 7x faster than pldexp_impl, but will prematurely over/underflow +// if 2^e doesn't fit into a normal floating-point Scalar. +// +// Assumes IEEE floating point format +template<typename Packet> +struct pldexp_fast_impl { + typedef typename unpacket_traits<Packet>::integer_packet PacketI; + typedef typename unpacket_traits<Packet>::type Scalar; + typedef typename unpacket_traits<PacketI>::type ScalarI; + enum { + TotalBits = sizeof(Scalar) * CHAR_BIT, + MantissaBits = numext::numeric_limits<Scalar>::digits - 1, + ExponentBits = int(TotalBits) - int(MantissaBits) - 1 + }; + + static EIGEN_STRONG_INLINE EIGEN_DEVICE_FUNC + Packet run(const Packet& a, const Packet& exponent) { + const Packet bias = pset1<Packet>(Scalar((ScalarI(1)<<(int(ExponentBits)-1)) - ScalarI(1))); // 127 + const Packet limit = pset1<Packet>(Scalar((ScalarI(1)<<int(ExponentBits)) - ScalarI(1))); // 255 + // restrict biased exponent between 0 and 255 for float. + const PacketI e = pcast<Packet, PacketI>(pmin(pmax(padd(exponent, bias), pzero(limit)), limit)); // exponent + 127 + // return a * (2^e) + return pmul(a, preinterpret<Packet>(plogical_shift_left<int(MantissaBits)>(e))); + } +}; + +// Natural or base 2 logarithm. +// Computes log(x) as log(2^e * m) = C*e + log(m), where the constant C =log(2) +// and m is in the range [sqrt(1/2),sqrt(2)). In this range, the logarithm can +// be easily approximated by a polynomial centered on m=1 for stability. +// TODO(gonnet): Further reduce the interval allowing for lower-degree +// polynomial interpolants -> ... -> profit! +template <typename Packet, bool base2> +EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS +EIGEN_UNUSED +Packet plog_impl_float(const Packet _x) +{ + Packet x = _x; + + const Packet cst_1 = pset1<Packet>(1.0f); + const Packet cst_neg_half = pset1<Packet>(-0.5f); + // The smallest non denormalized float number. + const Packet cst_min_norm_pos = pset1frombits<Packet>( 0x00800000u); + const Packet cst_minus_inf = pset1frombits<Packet>( 0xff800000u); + const Packet cst_pos_inf = pset1frombits<Packet>( 0x7f800000u); + + // Polynomial coefficients. + const Packet cst_cephes_SQRTHF = pset1<Packet>(0.707106781186547524f); + const Packet cst_cephes_log_p0 = pset1<Packet>(7.0376836292E-2f); + const Packet cst_cephes_log_p1 = pset1<Packet>(-1.1514610310E-1f); + const Packet cst_cephes_log_p2 = pset1<Packet>(1.1676998740E-1f); + const Packet cst_cephes_log_p3 = pset1<Packet>(-1.2420140846E-1f); + const Packet cst_cephes_log_p4 = pset1<Packet>(+1.4249322787E-1f); + const Packet cst_cephes_log_p5 = pset1<Packet>(-1.6668057665E-1f); + const Packet cst_cephes_log_p6 = pset1<Packet>(+2.0000714765E-1f); + const Packet cst_cephes_log_p7 = pset1<Packet>(-2.4999993993E-1f); + const Packet cst_cephes_log_p8 = pset1<Packet>(+3.3333331174E-1f); + + // Truncate input values to the minimum positive normal. + x = pmax(x, cst_min_norm_pos); + + Packet e; + // extract significant in the range [0.5,1) and exponent + x = pfrexp(x,e); + + // part2: Shift the inputs from the range [0.5,1) to [sqrt(1/2),sqrt(2)) + // and shift by -1. The values are then centered around 0, which improves + // the stability of the polynomial evaluation. + // if( x < SQRTHF ) { + // e -= 1; + // x = x + x - 1.0; + // } else { x = x - 1.0; } + Packet mask = pcmp_lt(x, cst_cephes_SQRTHF); + Packet tmp = pand(x, mask); + x = psub(x, cst_1); + e = psub(e, pand(cst_1, mask)); + x = padd(x, tmp); + + Packet x2 = pmul(x, x); + Packet x3 = pmul(x2, x); + + // Evaluate the polynomial approximant of degree 8 in three parts, probably + // to improve instruction-level parallelism. + Packet y, y1, y2; + y = pmadd(cst_cephes_log_p0, x, cst_cephes_log_p1); + y1 = pmadd(cst_cephes_log_p3, x, cst_cephes_log_p4); + y2 = pmadd(cst_cephes_log_p6, x, cst_cephes_log_p7); + y = pmadd(y, x, cst_cephes_log_p2); + y1 = pmadd(y1, x, cst_cephes_log_p5); + y2 = pmadd(y2, x, cst_cephes_log_p8); + y = pmadd(y, x3, y1); + y = pmadd(y, x3, y2); + y = pmul(y, x3); + + y = pmadd(cst_neg_half, x2, y); + x = padd(x, y); + + // Add the logarithm of the exponent back to the result of the interpolation. + if (base2) { + const Packet cst_log2e = pset1<Packet>(static_cast<float>(EIGEN_LOG2E)); + x = pmadd(x, cst_log2e, e); + } else { + const Packet cst_ln2 = pset1<Packet>(static_cast<float>(EIGEN_LN2)); + x = pmadd(e, cst_ln2, x); + } + + Packet invalid_mask = pcmp_lt_or_nan(_x, pzero(_x)); + Packet iszero_mask = pcmp_eq(_x,pzero(_x)); + Packet pos_inf_mask = pcmp_eq(_x,cst_pos_inf); + // Filter out invalid inputs, i.e.: + // - negative arg will be NAN + // - 0 will be -INF + // - +INF will be +INF + return pselect(iszero_mask, cst_minus_inf, + por(pselect(pos_inf_mask,cst_pos_inf,x), invalid_mask)); +} + +template <typename Packet> +EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS +EIGEN_UNUSED +Packet plog_float(const Packet _x) +{ + return plog_impl_float<Packet, /* base2 */ false>(_x); +} + +template <typename Packet> +EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS +EIGEN_UNUSED +Packet plog2_float(const Packet _x) +{ + return plog_impl_float<Packet, /* base2 */ true>(_x); +} + +/* Returns the base e (2.718...) or base 2 logarithm of x. + * The argument is separated into its exponent and fractional parts. + * The logarithm of the fraction in the interval [sqrt(1/2), sqrt(2)], + * is approximated by + * + * log(1+x) = x - 0.5 x**2 + x**3 P(x)/Q(x). + * + * for more detail see: http://www.netlib.org/cephes/ + */ +template <typename Packet, bool base2> +EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS +EIGEN_UNUSED +Packet plog_impl_double(const Packet _x) +{ + Packet x = _x; + + const Packet cst_1 = pset1<Packet>(1.0); + const Packet cst_neg_half = pset1<Packet>(-0.5); + // The smallest non denormalized double. + const Packet cst_min_norm_pos = pset1frombits<Packet>( static_cast<uint64_t>(0x0010000000000000ull)); + const Packet cst_minus_inf = pset1frombits<Packet>( static_cast<uint64_t>(0xfff0000000000000ull)); + const Packet cst_pos_inf = pset1frombits<Packet>( static_cast<uint64_t>(0x7ff0000000000000ull)); + + + // Polynomial Coefficients for log(1+x) = x - x**2/2 + x**3 P(x)/Q(x) + // 1/sqrt(2) <= x < sqrt(2) + const Packet cst_cephes_SQRTHF = pset1<Packet>(0.70710678118654752440E0); + const Packet cst_cephes_log_p0 = pset1<Packet>(1.01875663804580931796E-4); + const Packet cst_cephes_log_p1 = pset1<Packet>(4.97494994976747001425E-1); + const Packet cst_cephes_log_p2 = pset1<Packet>(4.70579119878881725854E0); + const Packet cst_cephes_log_p3 = pset1<Packet>(1.44989225341610930846E1); + const Packet cst_cephes_log_p4 = pset1<Packet>(1.79368678507819816313E1); + const Packet cst_cephes_log_p5 = pset1<Packet>(7.70838733755885391666E0); + + const Packet cst_cephes_log_q0 = pset1<Packet>(1.0); + const Packet cst_cephes_log_q1 = pset1<Packet>(1.12873587189167450590E1); + const Packet cst_cephes_log_q2 = pset1<Packet>(4.52279145837532221105E1); + const Packet cst_cephes_log_q3 = pset1<Packet>(8.29875266912776603211E1); + const Packet cst_cephes_log_q4 = pset1<Packet>(7.11544750618563894466E1); + const Packet cst_cephes_log_q5 = pset1<Packet>(2.31251620126765340583E1); + + // Truncate input values to the minimum positive normal. + x = pmax(x, cst_min_norm_pos); + + Packet e; + // extract significant in the range [0.5,1) and exponent + x = pfrexp(x,e); + + // Shift the inputs from the range [0.5,1) to [sqrt(1/2),sqrt(2)) + // and shift by -1. The values are then centered around 0, which improves + // the stability of the polynomial evaluation. + // if( x < SQRTHF ) { + // e -= 1; + // x = x + x - 1.0; + // } else { x = x - 1.0; } + Packet mask = pcmp_lt(x, cst_cephes_SQRTHF); + Packet tmp = pand(x, mask); + x = psub(x, cst_1); + e = psub(e, pand(cst_1, mask)); + x = padd(x, tmp); + + Packet x2 = pmul(x, x); + Packet x3 = pmul(x2, x); + + // Evaluate the polynomial approximant , probably to improve instruction-level parallelism. + // y = x - 0.5*x^2 + x^3 * polevl( x, P, 5 ) / p1evl( x, Q, 5 ) ); + Packet y, y1, y_; + y = pmadd(cst_cephes_log_p0, x, cst_cephes_log_p1); + y1 = pmadd(cst_cephes_log_p3, x, cst_cephes_log_p4); + y = pmadd(y, x, cst_cephes_log_p2); + y1 = pmadd(y1, x, cst_cephes_log_p5); + y_ = pmadd(y, x3, y1); + + y = pmadd(cst_cephes_log_q0, x, cst_cephes_log_q1); + y1 = pmadd(cst_cephes_log_q3, x, cst_cephes_log_q4); + y = pmadd(y, x, cst_cephes_log_q2); + y1 = pmadd(y1, x, cst_cephes_log_q5); + y = pmadd(y, x3, y1); + + y_ = pmul(y_, x3); + y = pdiv(y_, y); + + y = pmadd(cst_neg_half, x2, y); + x = padd(x, y); + + // Add the logarithm of the exponent back to the result of the interpolation. + if (base2) { + const Packet cst_log2e = pset1<Packet>(static_cast<double>(EIGEN_LOG2E)); + x = pmadd(x, cst_log2e, e); + } else { + const Packet cst_ln2 = pset1<Packet>(static_cast<double>(EIGEN_LN2)); + x = pmadd(e, cst_ln2, x); + } + + Packet invalid_mask = pcmp_lt_or_nan(_x, pzero(_x)); + Packet iszero_mask = pcmp_eq(_x,pzero(_x)); + Packet pos_inf_mask = pcmp_eq(_x,cst_pos_inf); + // Filter out invalid inputs, i.e.: + // - negative arg will be NAN + // - 0 will be -INF + // - +INF will be +INF + return pselect(iszero_mask, cst_minus_inf, + por(pselect(pos_inf_mask,cst_pos_inf,x), invalid_mask)); +} + +template <typename Packet> +EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS +EIGEN_UNUSED +Packet plog_double(const Packet _x) +{ + return plog_impl_double<Packet, /* base2 */ false>(_x); +} + +template <typename Packet> +EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS +EIGEN_UNUSED +Packet plog2_double(const Packet _x) +{ + return plog_impl_double<Packet, /* base2 */ true>(_x); +} + +/** \internal \returns log(1 + x) computed using W. Kahan's formula. + See: http://www.plunk.org/~hatch/rightway.php + */ +template<typename Packet> +Packet generic_plog1p(const Packet& x) +{ + typedef typename unpacket_traits<Packet>::type ScalarType; + const Packet one = pset1<Packet>(ScalarType(1)); + Packet xp1 = padd(x, one); + Packet small_mask = pcmp_eq(xp1, one); + Packet log1 = plog(xp1); + Packet inf_mask = pcmp_eq(xp1, log1); + Packet log_large = pmul(x, pdiv(log1, psub(xp1, one))); + return pselect(por(small_mask, inf_mask), x, log_large); +} + +/** \internal \returns exp(x)-1 computed using W. Kahan's formula. + See: http://www.plunk.org/~hatch/rightway.php + */ +template<typename Packet> +Packet generic_expm1(const Packet& x) +{ + typedef typename unpacket_traits<Packet>::type ScalarType; + const Packet one = pset1<Packet>(ScalarType(1)); + const Packet neg_one = pset1<Packet>(ScalarType(-1)); + Packet u = pexp(x); + Packet one_mask = pcmp_eq(u, one); + Packet u_minus_one = psub(u, one); + Packet neg_one_mask = pcmp_eq(u_minus_one, neg_one); + Packet logu = plog(u); + // The following comparison is to catch the case where + // exp(x) = +inf. It is written in this way to avoid having + // to form the constant +inf, which depends on the packet + // type. + Packet pos_inf_mask = pcmp_eq(logu, u); + Packet expm1 = pmul(u_minus_one, pdiv(x, logu)); + expm1 = pselect(pos_inf_mask, u, expm1); + return pselect(one_mask, + x, + pselect(neg_one_mask, + neg_one, + expm1)); +} + + +// Exponential function. Works by writing "x = m*log(2) + r" where +// "m = floor(x/log(2)+1/2)" and "r" is the remainder. The result is then +// "exp(x) = 2^m*exp(r)" where exp(r) is in the range [-1,1). +template <typename Packet> +EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS +EIGEN_UNUSED +Packet pexp_float(const Packet _x) +{ + const Packet cst_1 = pset1<Packet>(1.0f); + const Packet cst_half = pset1<Packet>(0.5f); + const Packet cst_exp_hi = pset1<Packet>( 88.723f); + const Packet cst_exp_lo = pset1<Packet>(-88.723f); + + const Packet cst_cephes_LOG2EF = pset1<Packet>(1.44269504088896341f); + const Packet cst_cephes_exp_p0 = pset1<Packet>(1.9875691500E-4f); + const Packet cst_cephes_exp_p1 = pset1<Packet>(1.3981999507E-3f); + const Packet cst_cephes_exp_p2 = pset1<Packet>(8.3334519073E-3f); + const Packet cst_cephes_exp_p3 = pset1<Packet>(4.1665795894E-2f); + const Packet cst_cephes_exp_p4 = pset1<Packet>(1.6666665459E-1f); + const Packet cst_cephes_exp_p5 = pset1<Packet>(5.0000001201E-1f); + + // Clamp x. + Packet x = pmax(pmin(_x, cst_exp_hi), cst_exp_lo); + + // Express exp(x) as exp(m*ln(2) + r), start by extracting + // m = floor(x/ln(2) + 0.5). + Packet m = pfloor(pmadd(x, cst_cephes_LOG2EF, cst_half)); + + // Get r = x - m*ln(2). If no FMA instructions are available, m*ln(2) is + // subtracted out in two parts, m*C1+m*C2 = m*ln(2), to avoid accumulating + // truncation errors. + const Packet cst_cephes_exp_C1 = pset1<Packet>(-0.693359375f); + const Packet cst_cephes_exp_C2 = pset1<Packet>(2.12194440e-4f); + Packet r = pmadd(m, cst_cephes_exp_C1, x); + r = pmadd(m, cst_cephes_exp_C2, r); + + Packet r2 = pmul(r, r); + Packet r3 = pmul(r2, r); + + // Evaluate the polynomial approximant,improved by instruction-level parallelism. + Packet y, y1, y2; + y = pmadd(cst_cephes_exp_p0, r, cst_cephes_exp_p1); + y1 = pmadd(cst_cephes_exp_p3, r, cst_cephes_exp_p4); + y2 = padd(r, cst_1); + y = pmadd(y, r, cst_cephes_exp_p2); + y1 = pmadd(y1, r, cst_cephes_exp_p5); + y = pmadd(y, r3, y1); + y = pmadd(y, r2, y2); + + // Return 2^m * exp(r). + // TODO: replace pldexp with faster implementation since y in [-1, 1). + return pmax(pldexp(y,m), _x); +} + +template <typename Packet> +EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS +EIGEN_UNUSED +Packet pexp_double(const Packet _x) +{ + Packet x = _x; + + const Packet cst_1 = pset1<Packet>(1.0); + const Packet cst_2 = pset1<Packet>(2.0); + const Packet cst_half = pset1<Packet>(0.5); + + const Packet cst_exp_hi = pset1<Packet>(709.784); + const Packet cst_exp_lo = pset1<Packet>(-709.784); + + const Packet cst_cephes_LOG2EF = pset1<Packet>(1.4426950408889634073599); + const Packet cst_cephes_exp_p0 = pset1<Packet>(1.26177193074810590878e-4); + const Packet cst_cephes_exp_p1 = pset1<Packet>(3.02994407707441961300e-2); + const Packet cst_cephes_exp_p2 = pset1<Packet>(9.99999999999999999910e-1); + const Packet cst_cephes_exp_q0 = pset1<Packet>(3.00198505138664455042e-6); + const Packet cst_cephes_exp_q1 = pset1<Packet>(2.52448340349684104192e-3); + const Packet cst_cephes_exp_q2 = pset1<Packet>(2.27265548208155028766e-1); + const Packet cst_cephes_exp_q3 = pset1<Packet>(2.00000000000000000009e0); + const Packet cst_cephes_exp_C1 = pset1<Packet>(0.693145751953125); + const Packet cst_cephes_exp_C2 = pset1<Packet>(1.42860682030941723212e-6); + + Packet tmp, fx; + + // clamp x + x = pmax(pmin(x, cst_exp_hi), cst_exp_lo); + // Express exp(x) as exp(g + n*log(2)). + fx = pmadd(cst_cephes_LOG2EF, x, cst_half); + + // Get the integer modulus of log(2), i.e. the "n" described above. + fx = pfloor(fx); + + // Get the remainder modulo log(2), i.e. the "g" described above. Subtract + // n*log(2) out in two steps, i.e. n*C1 + n*C2, C1+C2=log2 to get the last + // digits right. + tmp = pmul(fx, cst_cephes_exp_C1); + Packet z = pmul(fx, cst_cephes_exp_C2); + x = psub(x, tmp); + x = psub(x, z); + + Packet x2 = pmul(x, x); + + // Evaluate the numerator polynomial of the rational interpolant. + Packet px = cst_cephes_exp_p0; + px = pmadd(px, x2, cst_cephes_exp_p1); + px = pmadd(px, x2, cst_cephes_exp_p2); + px = pmul(px, x); + + // Evaluate the denominator polynomial of the rational interpolant. + Packet qx = cst_cephes_exp_q0; + qx = pmadd(qx, x2, cst_cephes_exp_q1); + qx = pmadd(qx, x2, cst_cephes_exp_q2); + qx = pmadd(qx, x2, cst_cephes_exp_q3); + + // I don't really get this bit, copied from the SSE2 routines, so... + // TODO(gonnet): Figure out what is going on here, perhaps find a better + // rational interpolant? + x = pdiv(px, psub(qx, px)); + x = pmadd(cst_2, x, cst_1); + + // Construct the result 2^n * exp(g) = e * x. The max is used to catch + // non-finite values in the input. + // TODO: replace pldexp with faster implementation since x in [-1, 1). + return pmax(pldexp(x,fx), _x); +} + +// The following code is inspired by the following stack-overflow answer: +// https://stackoverflow.com/questions/30463616/payne-hanek-algorithm-implementation-in-c/30465751#30465751 +// It has been largely optimized: +// - By-pass calls to frexp. +// - Aligned loads of required 96 bits of 2/pi. This is accomplished by +// (1) balancing the mantissa and exponent to the required bits of 2/pi are +// aligned on 8-bits, and (2) replicating the storage of the bits of 2/pi. +// - Avoid a branch in rounding and extraction of the remaining fractional part. +// Overall, I measured a speed up higher than x2 on x86-64. +inline float trig_reduce_huge (float xf, int *quadrant) +{ + using Eigen::numext::int32_t; + using Eigen::numext::uint32_t; + using Eigen::numext::int64_t; + using Eigen::numext::uint64_t; + + const double pio2_62 = 3.4061215800865545e-19; // pi/2 * 2^-62 + const uint64_t zero_dot_five = uint64_t(1) << 61; // 0.5 in 2.62-bit fixed-point foramt + + // 192 bits of 2/pi for Payne-Hanek reduction + // Bits are introduced by packet of 8 to enable aligned reads. + static const uint32_t two_over_pi [] = + { + 0x00000028, 0x000028be, 0x0028be60, 0x28be60db, + 0xbe60db93, 0x60db9391, 0xdb939105, 0x9391054a, + 0x91054a7f, 0x054a7f09, 0x4a7f09d5, 0x7f09d5f4, + 0x09d5f47d, 0xd5f47d4d, 0xf47d4d37, 0x7d4d3770, + 0x4d377036, 0x377036d8, 0x7036d8a5, 0x36d8a566, + 0xd8a5664f, 0xa5664f10, 0x664f10e4, 0x4f10e410, + 0x10e41000, 0xe4100000 + }; + + uint32_t xi = numext::bit_cast<uint32_t>(xf); + // Below, -118 = -126 + 8. + // -126 is to get the exponent, + // +8 is to enable alignment of 2/pi's bits on 8 bits. + // This is possible because the fractional part of x as only 24 meaningful bits. + uint32_t e = (xi >> 23) - 118; + // Extract the mantissa and shift it to align it wrt the exponent + xi = ((xi & 0x007fffffu)| 0x00800000u) << (e & 0x7); + + uint32_t i = e >> 3; + uint32_t twoopi_1 = two_over_pi[i-1]; + uint32_t twoopi_2 = two_over_pi[i+3]; + uint32_t twoopi_3 = two_over_pi[i+7]; + + // Compute x * 2/pi in 2.62-bit fixed-point format. + uint64_t p; + p = uint64_t(xi) * twoopi_3; + p = uint64_t(xi) * twoopi_2 + (p >> 32); + p = (uint64_t(xi * twoopi_1) << 32) + p; + + // Round to nearest: add 0.5 and extract integral part. + uint64_t q = (p + zero_dot_five) >> 62; + *quadrant = int(q); + // Now it remains to compute "r = x - q*pi/2" with high accuracy, + // since we have p=x/(pi/2) with high accuracy, we can more efficiently compute r as: + // r = (p-q)*pi/2, + // where the product can be be carried out with sufficient accuracy using double precision. + p -= q<<62; + return float(double(int64_t(p)) * pio2_62); +} + +template<bool ComputeSine,typename Packet> +EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS +EIGEN_UNUSED +#if EIGEN_GNUC_AT_LEAST(4,4) && EIGEN_COMP_GNUC_STRICT +__attribute__((optimize("-fno-unsafe-math-optimizations"))) +#endif +Packet psincos_float(const Packet& _x) +{ + typedef typename unpacket_traits<Packet>::integer_packet PacketI; + + const Packet cst_2oPI = pset1<Packet>(0.636619746685028076171875f); // 2/PI + const Packet cst_rounding_magic = pset1<Packet>(12582912); // 2^23 for rounding + const PacketI csti_1 = pset1<PacketI>(1); + const Packet cst_sign_mask = pset1frombits<Packet>(0x80000000u); + + Packet x = pabs(_x); + + // Scale x by 2/Pi to find x's octant. + Packet y = pmul(x, cst_2oPI); + + // Rounding trick: + Packet y_round = padd(y, cst_rounding_magic); + EIGEN_OPTIMIZATION_BARRIER(y_round) + PacketI y_int = preinterpret<PacketI>(y_round); // last 23 digits represent integer (if abs(x)<2^24) + y = psub(y_round, cst_rounding_magic); // nearest integer to x*4/pi + + // Reduce x by y octants to get: -Pi/4 <= x <= +Pi/4 + // using "Extended precision modular arithmetic" + #if defined(EIGEN_HAS_SINGLE_INSTRUCTION_MADD) + // This version requires true FMA for high accuracy + // It provides a max error of 1ULP up to (with absolute_error < 5.9605e-08): + const float huge_th = ComputeSine ? 117435.992f : 71476.0625f; + x = pmadd(y, pset1<Packet>(-1.57079601287841796875f), x); + x = pmadd(y, pset1<Packet>(-3.1391647326017846353352069854736328125e-07f), x); + x = pmadd(y, pset1<Packet>(-5.390302529957764765544681040410068817436695098876953125e-15f), x); + #else + // Without true FMA, the previous set of coefficients maintain 1ULP accuracy + // up to x<15.7 (for sin), but accuracy is immediately lost for x>15.7. + // We thus use one more iteration to maintain 2ULPs up to reasonably large inputs. + + // The following set of coefficients maintain 1ULP up to 9.43 and 14.16 for sin and cos respectively. + // and 2 ULP up to: + const float huge_th = ComputeSine ? 25966.f : 18838.f; + x = pmadd(y, pset1<Packet>(-1.5703125), x); // = 0xbfc90000 + EIGEN_OPTIMIZATION_BARRIER(x) + x = pmadd(y, pset1<Packet>(-0.000483989715576171875), x); // = 0xb9fdc000 + EIGEN_OPTIMIZATION_BARRIER(x) + x = pmadd(y, pset1<Packet>(1.62865035235881805419921875e-07), x); // = 0x342ee000 + x = pmadd(y, pset1<Packet>(5.5644315544167710640977020375430583953857421875e-11), x); // = 0x2e74b9ee + + // For the record, the following set of coefficients maintain 2ULP up + // to a slightly larger range: + // const float huge_th = ComputeSine ? 51981.f : 39086.125f; + // but it slightly fails to maintain 1ULP for two values of sin below pi. + // x = pmadd(y, pset1<Packet>(-3.140625/2.), x); + // x = pmadd(y, pset1<Packet>(-0.00048351287841796875), x); + // x = pmadd(y, pset1<Packet>(-3.13855707645416259765625e-07), x); + // x = pmadd(y, pset1<Packet>(-6.0771006282767103812147979624569416046142578125e-11), x); + + // For the record, with only 3 iterations it is possible to maintain + // 1 ULP up to 3PI (maybe more) and 2ULP up to 255. + // The coefficients are: 0xbfc90f80, 0xb7354480, 0x2e74b9ee + #endif + + if(predux_any(pcmp_le(pset1<Packet>(huge_th),pabs(_x)))) + { + const int PacketSize = unpacket_traits<Packet>::size; + EIGEN_ALIGN_TO_BOUNDARY(sizeof(Packet)) float vals[PacketSize]; + EIGEN_ALIGN_TO_BOUNDARY(sizeof(Packet)) float x_cpy[PacketSize]; + EIGEN_ALIGN_TO_BOUNDARY(sizeof(Packet)) int y_int2[PacketSize]; + pstoreu(vals, pabs(_x)); + pstoreu(x_cpy, x); + pstoreu(y_int2, y_int); + for(int k=0; k<PacketSize;++k) + { + float val = vals[k]; + if(val>=huge_th && (numext::isfinite)(val)) + x_cpy[k] = trig_reduce_huge(val,&y_int2[k]); + } + x = ploadu<Packet>(x_cpy); + y_int = ploadu<PacketI>(y_int2); + } + + // Compute the sign to apply to the polynomial. + // sin: sign = second_bit(y_int) xor signbit(_x) + // cos: sign = second_bit(y_int+1) + Packet sign_bit = ComputeSine ? pxor(_x, preinterpret<Packet>(plogical_shift_left<30>(y_int))) + : preinterpret<Packet>(plogical_shift_left<30>(padd(y_int,csti_1))); + sign_bit = pand(sign_bit, cst_sign_mask); // clear all but left most bit + + // Get the polynomial selection mask from the second bit of y_int + // We'll calculate both (sin and cos) polynomials and then select from the two. + Packet poly_mask = preinterpret<Packet>(pcmp_eq(pand(y_int, csti_1), pzero(y_int))); + + Packet x2 = pmul(x,x); + + // Evaluate the cos(x) polynomial. (-Pi/4 <= x <= Pi/4) + Packet y1 = pset1<Packet>(2.4372266125283204019069671630859375e-05f); + y1 = pmadd(y1, x2, pset1<Packet>(-0.00138865201734006404876708984375f )); + y1 = pmadd(y1, x2, pset1<Packet>(0.041666619479656219482421875f )); + y1 = pmadd(y1, x2, pset1<Packet>(-0.5f)); + y1 = pmadd(y1, x2, pset1<Packet>(1.f)); + + // Evaluate the sin(x) polynomial. (Pi/4 <= x <= Pi/4) + // octave/matlab code to compute those coefficients: + // x = (0:0.0001:pi/4)'; + // A = [x.^3 x.^5 x.^7]; + // w = ((1.-(x/(pi/4)).^2).^5)*2000+1; # weights trading relative accuracy + // c = (A'*diag(w)*A)\(A'*diag(w)*(sin(x)-x)); # weighted LS, linear coeff forced to 1 + // printf('%.64f\n %.64f\n%.64f\n', c(3), c(2), c(1)) + // + Packet y2 = pset1<Packet>(-0.0001959234114083702898469196984621021329076029360294342041015625f); + y2 = pmadd(y2, x2, pset1<Packet>( 0.0083326873655616851693794799871284340042620897293090820312500000f)); + y2 = pmadd(y2, x2, pset1<Packet>(-0.1666666203982298255503735617821803316473960876464843750000000000f)); + y2 = pmul(y2, x2); + y2 = pmadd(y2, x, x); + + // Select the correct result from the two polynomials. + y = ComputeSine ? pselect(poly_mask,y2,y1) + : pselect(poly_mask,y1,y2); + + // Update the sign and filter huge inputs + return pxor(y, sign_bit); +} + +template<typename Packet> +EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS +EIGEN_UNUSED +Packet psin_float(const Packet& x) +{ + return psincos_float<true>(x); +} + +template<typename Packet> +EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS +EIGEN_UNUSED +Packet pcos_float(const Packet& x) +{ + return psincos_float<false>(x); +} + + +template<typename Packet> +EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS +EIGEN_UNUSED +Packet psqrt_complex(const Packet& a) { + typedef typename unpacket_traits<Packet>::type Scalar; + typedef typename Scalar::value_type RealScalar; + typedef typename unpacket_traits<Packet>::as_real RealPacket; + + // Computes the principal sqrt of the complex numbers in the input. + // + // For example, for packets containing 2 complex numbers stored in interleaved format + // a = [a0, a1] = [x0, y0, x1, y1], + // where x0 = real(a0), y0 = imag(a0) etc., this function returns + // b = [b0, b1] = [u0, v0, u1, v1], + // such that b0^2 = a0, b1^2 = a1. + // + // To derive the formula for the complex square roots, let's consider the equation for + // a single complex square root of the number x + i*y. We want to find real numbers + // u and v such that + // (u + i*v)^2 = x + i*y <=> + // u^2 - v^2 + i*2*u*v = x + i*v. + // By equating the real and imaginary parts we get: + // u^2 - v^2 = x + // 2*u*v = y. + // + // For x >= 0, this has the numerically stable solution + // u = sqrt(0.5 * (x + sqrt(x^2 + y^2))) + // v = 0.5 * (y / u) + // and for x < 0, + // v = sign(y) * sqrt(0.5 * (-x + sqrt(x^2 + y^2))) + // u = 0.5 * (y / v) + // + // To avoid unnecessary over- and underflow, we compute sqrt(x^2 + y^2) as + // l = max(|x|, |y|) * sqrt(1 + (min(|x|, |y|) / max(|x|, |y|))^2) , + + // In the following, without lack of generality, we have annotated the code, assuming + // that the input is a packet of 2 complex numbers. + // + // Step 1. Compute l = [l0, l0, l1, l1], where + // l0 = sqrt(x0^2 + y0^2), l1 = sqrt(x1^2 + y1^2) + // To avoid over- and underflow, we use the stable formula for each hypotenuse + // l0 = (min0 == 0 ? max0 : max0 * sqrt(1 + (min0/max0)**2)), + // where max0 = max(|x0|, |y0|), min0 = min(|x0|, |y0|), and similarly for l1. + + RealPacket a_abs = pabs(a.v); // [|x0|, |y0|, |x1|, |y1|] + RealPacket a_abs_flip = pcplxflip(Packet(a_abs)).v; // [|y0|, |x0|, |y1|, |x1|] + RealPacket a_max = pmax(a_abs, a_abs_flip); + RealPacket a_min = pmin(a_abs, a_abs_flip); + RealPacket a_min_zero_mask = pcmp_eq(a_min, pzero(a_min)); + RealPacket a_max_zero_mask = pcmp_eq(a_max, pzero(a_max)); + RealPacket r = pdiv(a_min, a_max); + const RealPacket cst_one = pset1<RealPacket>(RealScalar(1)); + RealPacket l = pmul(a_max, psqrt(padd(cst_one, pmul(r, r)))); // [l0, l0, l1, l1] + // Set l to a_max if a_min is zero. + l = pselect(a_min_zero_mask, a_max, l); + + // Step 2. Compute [rho0, *, rho1, *], where + // rho0 = sqrt(0.5 * (l0 + |x0|)), rho1 = sqrt(0.5 * (l1 + |x1|)) + // We don't care about the imaginary parts computed here. They will be overwritten later. + const RealPacket cst_half = pset1<RealPacket>(RealScalar(0.5)); + Packet rho; + rho.v = psqrt(pmul(cst_half, padd(a_abs, l))); + + // Step 3. Compute [rho0, eta0, rho1, eta1], where + // eta0 = (y0 / l0) / 2, and eta1 = (y1 / l1) / 2. + // set eta = 0 of input is 0 + i0. + RealPacket eta = pandnot(pmul(cst_half, pdiv(a.v, pcplxflip(rho).v)), a_max_zero_mask); + RealPacket real_mask = peven_mask(a.v); + Packet positive_real_result; + // Compute result for inputs with positive real part. + positive_real_result.v = pselect(real_mask, rho.v, eta); + + // Step 4. Compute solution for inputs with negative real part: + // [|eta0|, sign(y0)*rho0, |eta1|, sign(y1)*rho1] + const RealScalar neg_zero = RealScalar(numext::bit_cast<float>(0x80000000u)); + const RealPacket cst_imag_sign_mask = pset1<Packet>(Scalar(RealScalar(0.0), neg_zero)).v; + RealPacket imag_signs = pand(a.v, cst_imag_sign_mask); + Packet negative_real_result; + // Notice that rho is positive, so taking it's absolute value is a noop. + negative_real_result.v = por(pabs(pcplxflip(positive_real_result).v), imag_signs); + + // Step 5. Select solution branch based on the sign of the real parts. + Packet negative_real_mask; + negative_real_mask.v = pcmp_lt(pand(real_mask, a.v), pzero(a.v)); + negative_real_mask.v = por(negative_real_mask.v, pcplxflip(negative_real_mask).v); + Packet result = pselect(negative_real_mask, negative_real_result, positive_real_result); + + // Step 6. Handle special cases for infinities: + // * If z is (x,+∞), the result is (+∞,+∞) even if x is NaN + // * If z is (x,-∞), the result is (+∞,-∞) even if x is NaN + // * If z is (-∞,y), the result is (0*|y|,+∞) for finite or NaN y + // * If z is (+∞,y), the result is (+∞,0*|y|) for finite or NaN y + const RealPacket cst_pos_inf = pset1<RealPacket>(NumTraits<RealScalar>::infinity()); + Packet is_inf; + is_inf.v = pcmp_eq(a_abs, cst_pos_inf); + Packet is_real_inf; + is_real_inf.v = pand(is_inf.v, real_mask); + is_real_inf = por(is_real_inf, pcplxflip(is_real_inf)); + // prepare packet of (+∞,0*|y|) or (0*|y|,+∞), depending on the sign of the infinite real part. + Packet real_inf_result; + real_inf_result.v = pmul(a_abs, pset1<Packet>(Scalar(RealScalar(1.0), RealScalar(0.0))).v); + real_inf_result.v = pselect(negative_real_mask.v, pcplxflip(real_inf_result).v, real_inf_result.v); + // prepare packet of (+∞,+∞) or (+∞,-∞), depending on the sign of the infinite imaginary part. + Packet is_imag_inf; + is_imag_inf.v = pandnot(is_inf.v, real_mask); + is_imag_inf = por(is_imag_inf, pcplxflip(is_imag_inf)); + Packet imag_inf_result; + imag_inf_result.v = por(pand(cst_pos_inf, real_mask), pandnot(a.v, real_mask)); + + return pselect(is_imag_inf, imag_inf_result, + pselect(is_real_inf, real_inf_result,result)); +} + +// TODO(rmlarsen): The following set of utilities for double word arithmetic +// should perhaps be refactored as a separate file, since it would be generally +// useful for special function implementation etc. Writing the algorithms in +// terms if a double word type would also make the code more readable. + +// This function splits x into the nearest integer n and fractional part r, +// such that x = n + r holds exactly. +template<typename Packet> +EIGEN_STRONG_INLINE +void absolute_split(const Packet& x, Packet& n, Packet& r) { + n = pround(x); + r = psub(x, n); +} + +// This function computes the sum {s, r}, such that x + y = s_hi + s_lo +// holds exactly, and s_hi = fl(x+y), if |x| >= |y|. +template<typename Packet> +EIGEN_STRONG_INLINE +void fast_twosum(const Packet& x, const Packet& y, Packet& s_hi, Packet& s_lo) { + s_hi = padd(x, y); + const Packet t = psub(s_hi, x); + s_lo = psub(y, t); +} + +#ifdef EIGEN_HAS_SINGLE_INSTRUCTION_MADD +// This function implements the extended precision product of +// a pair of floating point numbers. Given {x, y}, it computes the pair +// {p_hi, p_lo} such that x * y = p_hi + p_lo holds exactly and +// p_hi = fl(x * y). +template<typename Packet> +EIGEN_STRONG_INLINE +void twoprod(const Packet& x, const Packet& y, + Packet& p_hi, Packet& p_lo) { + p_hi = pmul(x, y); + p_lo = pmadd(x, y, pnegate(p_hi)); +} + +#else + +// This function implements the Veltkamp splitting. Given a floating point +// number x it returns the pair {x_hi, x_lo} such that x_hi + x_lo = x holds +// exactly and that half of the significant of x fits in x_hi. +// This is Algorithm 3 from Jean-Michel Muller, "Elementary Functions", +// 3rd edition, Birkh\"auser, 2016. +template<typename Packet> +EIGEN_STRONG_INLINE +void veltkamp_splitting(const Packet& x, Packet& x_hi, Packet& x_lo) { + typedef typename unpacket_traits<Packet>::type Scalar; + EIGEN_CONSTEXPR int shift = (NumTraits<Scalar>::digits() + 1) / 2; + const Scalar shift_scale = Scalar(uint64_t(1) << shift); // Scalar constructor not necessarily constexpr. + const Packet gamma = pmul(pset1<Packet>(shift_scale + Scalar(1)), x); + Packet rho = psub(x, gamma); + x_hi = padd(rho, gamma); + x_lo = psub(x, x_hi); +} + +// This function implements Dekker's algorithm for products x * y. +// Given floating point numbers {x, y} computes the pair +// {p_hi, p_lo} such that x * y = p_hi + p_lo holds exactly and +// p_hi = fl(x * y). +template<typename Packet> +EIGEN_STRONG_INLINE +void twoprod(const Packet& x, const Packet& y, + Packet& p_hi, Packet& p_lo) { + Packet x_hi, x_lo, y_hi, y_lo; + veltkamp_splitting(x, x_hi, x_lo); + veltkamp_splitting(y, y_hi, y_lo); + + p_hi = pmul(x, y); + p_lo = pmadd(x_hi, y_hi, pnegate(p_hi)); + p_lo = pmadd(x_hi, y_lo, p_lo); + p_lo = pmadd(x_lo, y_hi, p_lo); + p_lo = pmadd(x_lo, y_lo, p_lo); +} + +#endif // EIGEN_HAS_SINGLE_INSTRUCTION_MADD + + +// This function implements Dekker's algorithm for the addition +// of two double word numbers represented by {x_hi, x_lo} and {y_hi, y_lo}. +// It returns the result as a pair {s_hi, s_lo} such that +// x_hi + x_lo + y_hi + y_lo = s_hi + s_lo holds exactly. +// This is Algorithm 5 from Jean-Michel Muller, "Elementary Functions", +// 3rd edition, Birkh\"auser, 2016. +template<typename Packet> +EIGEN_STRONG_INLINE + void twosum(const Packet& x_hi, const Packet& x_lo, + const Packet& y_hi, const Packet& y_lo, + Packet& s_hi, Packet& s_lo) { + const Packet x_greater_mask = pcmp_lt(pabs(y_hi), pabs(x_hi)); + Packet r_hi_1, r_lo_1; + fast_twosum(x_hi, y_hi,r_hi_1, r_lo_1); + Packet r_hi_2, r_lo_2; + fast_twosum(y_hi, x_hi,r_hi_2, r_lo_2); + const Packet r_hi = pselect(x_greater_mask, r_hi_1, r_hi_2); + + const Packet s1 = padd(padd(y_lo, r_lo_1), x_lo); + const Packet s2 = padd(padd(x_lo, r_lo_2), y_lo); + const Packet s = pselect(x_greater_mask, s1, s2); + + fast_twosum(r_hi, s, s_hi, s_lo); +} + +// This is a version of twosum for double word numbers, +// which assumes that |x_hi| >= |y_hi|. +template<typename Packet> +EIGEN_STRONG_INLINE + void fast_twosum(const Packet& x_hi, const Packet& x_lo, + const Packet& y_hi, const Packet& y_lo, + Packet& s_hi, Packet& s_lo) { + Packet r_hi, r_lo; + fast_twosum(x_hi, y_hi, r_hi, r_lo); + const Packet s = padd(padd(y_lo, r_lo), x_lo); + fast_twosum(r_hi, s, s_hi, s_lo); +} + +// This is a version of twosum for adding a floating point number x to +// double word number {y_hi, y_lo} number, with the assumption +// that |x| >= |y_hi|. +template<typename Packet> +EIGEN_STRONG_INLINE +void fast_twosum(const Packet& x, + const Packet& y_hi, const Packet& y_lo, + Packet& s_hi, Packet& s_lo) { + Packet r_hi, r_lo; + fast_twosum(x, y_hi, r_hi, r_lo); + const Packet s = padd(y_lo, r_lo); + fast_twosum(r_hi, s, s_hi, s_lo); +} + +// This function implements the multiplication of a double word +// number represented by {x_hi, x_lo} by a floating point number y. +// It returns the result as a pair {p_hi, p_lo} such that +// (x_hi + x_lo) * y = p_hi + p_lo hold with a relative error +// of less than 2*2^{-2p}, where p is the number of significand bit +// in the floating point type. +// This is Algorithm 7 from Jean-Michel Muller, "Elementary Functions", +// 3rd edition, Birkh\"auser, 2016. +template<typename Packet> +EIGEN_STRONG_INLINE +void twoprod(const Packet& x_hi, const Packet& x_lo, const Packet& y, + Packet& p_hi, Packet& p_lo) { + Packet c_hi, c_lo1; + twoprod(x_hi, y, c_hi, c_lo1); + const Packet c_lo2 = pmul(x_lo, y); + Packet t_hi, t_lo1; + fast_twosum(c_hi, c_lo2, t_hi, t_lo1); + const Packet t_lo2 = padd(t_lo1, c_lo1); + fast_twosum(t_hi, t_lo2, p_hi, p_lo); +} + +// This function implements the multiplication of two double word +// numbers represented by {x_hi, x_lo} and {y_hi, y_lo}. +// It returns the result as a pair {p_hi, p_lo} such that +// (x_hi + x_lo) * (y_hi + y_lo) = p_hi + p_lo holds with a relative error +// of less than 2*2^{-2p}, where p is the number of significand bit +// in the floating point type. +template<typename Packet> +EIGEN_STRONG_INLINE +void twoprod(const Packet& x_hi, const Packet& x_lo, + const Packet& y_hi, const Packet& y_lo, + Packet& p_hi, Packet& p_lo) { + Packet p_hi_hi, p_hi_lo; + twoprod(x_hi, x_lo, y_hi, p_hi_hi, p_hi_lo); + Packet p_lo_hi, p_lo_lo; + twoprod(x_hi, x_lo, y_lo, p_lo_hi, p_lo_lo); + fast_twosum(p_hi_hi, p_hi_lo, p_lo_hi, p_lo_lo, p_hi, p_lo); +} + +// This function computes the reciprocal of a floating point number +// with extra precision and returns the result as a double word. +template <typename Packet> +void doubleword_reciprocal(const Packet& x, Packet& recip_hi, Packet& recip_lo) { + typedef typename unpacket_traits<Packet>::type Scalar; + // 1. Approximate the reciprocal as the reciprocal of the high order element. + Packet approx_recip = prsqrt(x); + approx_recip = pmul(approx_recip, approx_recip); + + // 2. Run one step of Newton-Raphson iteration in double word arithmetic + // to get the bottom half. The NR iteration for reciprocal of 'a' is + // x_{i+1} = x_i * (2 - a * x_i) + + // -a*x_i + Packet t1_hi, t1_lo; + twoprod(pnegate(x), approx_recip, t1_hi, t1_lo); + // 2 - a*x_i + Packet t2_hi, t2_lo; + fast_twosum(pset1<Packet>(Scalar(2)), t1_hi, t2_hi, t2_lo); + Packet t3_hi, t3_lo; + fast_twosum(t2_hi, padd(t2_lo, t1_lo), t3_hi, t3_lo); + // x_i * (2 - a * x_i) + twoprod(t3_hi, t3_lo, approx_recip, recip_hi, recip_lo); +} + + +// This function computes log2(x) and returns the result as a double word. +template <typename Scalar> +struct accurate_log2 { + template <typename Packet> + EIGEN_STRONG_INLINE + void operator()(const Packet& x, Packet& log2_x_hi, Packet& log2_x_lo) { + log2_x_hi = plog2(x); + log2_x_lo = pzero(x); + } +}; + +// This specialization uses a more accurate algorithm to compute log2(x) for +// floats in [1/sqrt(2);sqrt(2)] with a relative accuracy of ~6.42e-10. +// This additional accuracy is needed to counter the error-magnification +// inherent in multiplying by a potentially large exponent in pow(x,y). +// The minimax polynomial used was calculated using the Sollya tool. +// See sollya.org. +template <> +struct accurate_log2<float> { + template <typename Packet> + EIGEN_STRONG_INLINE + void operator()(const Packet& z, Packet& log2_x_hi, Packet& log2_x_lo) { + // The function log(1+x)/x is approximated in the interval + // [1/sqrt(2)-1;sqrt(2)-1] by a degree 10 polynomial of the form + // Q(x) = (C0 + x * (C1 + x * (C2 + x * (C3 + x * P(x))))), + // where the degree 6 polynomial P(x) is evaluated in single precision, + // while the remaining 4 terms of Q(x), as well as the final multiplication by x + // to reconstruct log(1+x) are evaluated in extra precision using + // double word arithmetic. C0 through C3 are extra precise constants + // stored as double words. + // + // The polynomial coefficients were calculated using Sollya commands: + // > n = 10; + // > f = log2(1+x)/x; + // > interval = [sqrt(0.5)-1;sqrt(2)-1]; + // > p = fpminimax(f,n,[|double,double,double,double,single...|],interval,relative,floating); + + const Packet p6 = pset1<Packet>( 9.703654795885e-2f); + const Packet p5 = pset1<Packet>(-0.1690667718648f); + const Packet p4 = pset1<Packet>( 0.1720575392246f); + const Packet p3 = pset1<Packet>(-0.1789081543684f); + const Packet p2 = pset1<Packet>( 0.2050433009862f); + const Packet p1 = pset1<Packet>(-0.2404672354459f); + const Packet p0 = pset1<Packet>( 0.2885761857032f); + + const Packet C3_hi = pset1<Packet>(-0.360674142838f); + const Packet C3_lo = pset1<Packet>(-6.13283912543e-09f); + const Packet C2_hi = pset1<Packet>(0.480897903442f); + const Packet C2_lo = pset1<Packet>(-1.44861207474e-08f); + const Packet C1_hi = pset1<Packet>(-0.721347510815f); + const Packet C1_lo = pset1<Packet>(-4.84483164698e-09f); + const Packet C0_hi = pset1<Packet>(1.44269502163f); + const Packet C0_lo = pset1<Packet>(2.01711713999e-08f); + const Packet one = pset1<Packet>(1.0f); + + const Packet x = psub(z, one); + // Evaluate P(x) in working precision. + // We evaluate it in multiple parts to improve instruction level + // parallelism. + Packet x2 = pmul(x,x); + Packet p_even = pmadd(p6, x2, p4); + p_even = pmadd(p_even, x2, p2); + p_even = pmadd(p_even, x2, p0); + Packet p_odd = pmadd(p5, x2, p3); + p_odd = pmadd(p_odd, x2, p1); + Packet p = pmadd(p_odd, x, p_even); + + // Now evaluate the low-order tems of Q(x) in double word precision. + // In the following, due to the alternating signs and the fact that + // |x| < sqrt(2)-1, we can assume that |C*_hi| >= q_i, and use + // fast_twosum instead of the slower twosum. + Packet q_hi, q_lo; + Packet t_hi, t_lo; + // C3 + x * p(x) + twoprod(p, x, t_hi, t_lo); + fast_twosum(C3_hi, C3_lo, t_hi, t_lo, q_hi, q_lo); + // C2 + x * p(x) + twoprod(q_hi, q_lo, x, t_hi, t_lo); + fast_twosum(C2_hi, C2_lo, t_hi, t_lo, q_hi, q_lo); + // C1 + x * p(x) + twoprod(q_hi, q_lo, x, t_hi, t_lo); + fast_twosum(C1_hi, C1_lo, t_hi, t_lo, q_hi, q_lo); + // C0 + x * p(x) + twoprod(q_hi, q_lo, x, t_hi, t_lo); + fast_twosum(C0_hi, C0_lo, t_hi, t_lo, q_hi, q_lo); + + // log(z) ~= x * Q(x) + twoprod(q_hi, q_lo, x, log2_x_hi, log2_x_lo); + } +}; + +// This specialization uses a more accurate algorithm to compute log2(x) for +// floats in [1/sqrt(2);sqrt(2)] with a relative accuracy of ~1.27e-18. +// This additional accuracy is needed to counter the error-magnification +// inherent in multiplying by a potentially large exponent in pow(x,y). +// The minimax polynomial used was calculated using the Sollya tool. +// See sollya.org. + +template <> +struct accurate_log2<double> { + template <typename Packet> + EIGEN_STRONG_INLINE + void operator()(const Packet& x, Packet& log2_x_hi, Packet& log2_x_lo) { + // We use a transformation of variables: + // r = c * (x-1) / (x+1), + // such that + // log2(x) = log2((1 + r/c) / (1 - r/c)) = f(r). + // The function f(r) can be approximated well using an odd polynomial + // of the form + // P(r) = ((Q(r^2) * r^2 + C) * r^2 + 1) * r, + // For the implementation of log2<double> here, Q is of degree 6 with + // coefficient represented in working precision (double), while C is a + // constant represented in extra precision as a double word to achieve + // full accuracy. + // + // The polynomial coefficients were computed by the Sollya script: + // + // c = 2 / log(2); + // trans = c * (x-1)/(x+1); + // itrans = (1+x/c)/(1-x/c); + // interval=[trans(sqrt(0.5)); trans(sqrt(2))]; + // print(interval); + // f = log2(itrans(x)); + // p=fpminimax(f,[|1,3,5,7,9,11,13,15,17|],[|1,DD,double...|],interval,relative,floating); + const Packet q12 = pset1<Packet>(2.87074255468000586e-9); + const Packet q10 = pset1<Packet>(2.38957980901884082e-8); + const Packet q8 = pset1<Packet>(2.31032094540014656e-7); + const Packet q6 = pset1<Packet>(2.27279857398537278e-6); + const Packet q4 = pset1<Packet>(2.31271023278625638e-5); + const Packet q2 = pset1<Packet>(2.47556738444535513e-4); + const Packet q0 = pset1<Packet>(2.88543873228900172e-3); + const Packet C_hi = pset1<Packet>(0.0400377511598501157); + const Packet C_lo = pset1<Packet>(-4.77726582251425391e-19); + const Packet one = pset1<Packet>(1.0); + + const Packet cst_2_log2e_hi = pset1<Packet>(2.88539008177792677); + const Packet cst_2_log2e_lo = pset1<Packet>(4.07660016854549667e-17); + // c * (x - 1) + Packet num_hi, num_lo; + twoprod(cst_2_log2e_hi, cst_2_log2e_lo, psub(x, one), num_hi, num_lo); + // TODO(rmlarsen): Investigate if using the division algorithm by + // Muller et al. is faster/more accurate. + // 1 / (x + 1) + Packet denom_hi, denom_lo; + doubleword_reciprocal(padd(x, one), denom_hi, denom_lo); + // r = c * (x-1) / (x+1), + Packet r_hi, r_lo; + twoprod(num_hi, num_lo, denom_hi, denom_lo, r_hi, r_lo); + // r2 = r * r + Packet r2_hi, r2_lo; + twoprod(r_hi, r_lo, r_hi, r_lo, r2_hi, r2_lo); + // r4 = r2 * r2 + Packet r4_hi, r4_lo; + twoprod(r2_hi, r2_lo, r2_hi, r2_lo, r4_hi, r4_lo); + + // Evaluate Q(r^2) in working precision. We evaluate it in two parts + // (even and odd in r^2) to improve instruction level parallelism. + Packet q_even = pmadd(q12, r4_hi, q8); + Packet q_odd = pmadd(q10, r4_hi, q6); + q_even = pmadd(q_even, r4_hi, q4); + q_odd = pmadd(q_odd, r4_hi, q2); + q_even = pmadd(q_even, r4_hi, q0); + Packet q = pmadd(q_odd, r2_hi, q_even); + + // Now evaluate the low order terms of P(x) in double word precision. + // In the following, due to the increasing magnitude of the coefficients + // and r being constrained to [-0.5, 0.5] we can use fast_twosum instead + // of the slower twosum. + // Q(r^2) * r^2 + Packet p_hi, p_lo; + twoprod(r2_hi, r2_lo, q, p_hi, p_lo); + // Q(r^2) * r^2 + C + Packet p1_hi, p1_lo; + fast_twosum(C_hi, C_lo, p_hi, p_lo, p1_hi, p1_lo); + // (Q(r^2) * r^2 + C) * r^2 + Packet p2_hi, p2_lo; + twoprod(r2_hi, r2_lo, p1_hi, p1_lo, p2_hi, p2_lo); + // ((Q(r^2) * r^2 + C) * r^2 + 1) + Packet p3_hi, p3_lo; + fast_twosum(one, p2_hi, p2_lo, p3_hi, p3_lo); + + // log(z) ~= ((Q(r^2) * r^2 + C) * r^2 + 1) * r + twoprod(p3_hi, p3_lo, r_hi, r_lo, log2_x_hi, log2_x_lo); + } +}; + +// This function computes exp2(x) (i.e. 2**x). +template <typename Scalar> +struct fast_accurate_exp2 { + template <typename Packet> + EIGEN_STRONG_INLINE + Packet operator()(const Packet& x) { + // TODO(rmlarsen): Add a pexp2 packetop. + return pexp(pmul(pset1<Packet>(Scalar(EIGEN_LN2)), x)); + } +}; + +// This specialization uses a faster algorithm to compute exp2(x) for floats +// in [-0.5;0.5] with a relative accuracy of 1 ulp. +// The minimax polynomial used was calculated using the Sollya tool. +// See sollya.org. +template <> +struct fast_accurate_exp2<float> { + template <typename Packet> + EIGEN_STRONG_INLINE + Packet operator()(const Packet& x) { + // This function approximates exp2(x) by a degree 6 polynomial of the form + // Q(x) = 1 + x * (C + x * P(x)), where the degree 4 polynomial P(x) is evaluated in + // single precision, and the remaining steps are evaluated with extra precision using + // double word arithmetic. C is an extra precise constant stored as a double word. + // + // The polynomial coefficients were calculated using Sollya commands: + // > n = 6; + // > f = 2^x; + // > interval = [-0.5;0.5]; + // > p = fpminimax(f,n,[|1,double,single...|],interval,relative,floating); + + const Packet p4 = pset1<Packet>(1.539513905e-4f); + const Packet p3 = pset1<Packet>(1.340007293e-3f); + const Packet p2 = pset1<Packet>(9.618283249e-3f); + const Packet p1 = pset1<Packet>(5.550328270e-2f); + const Packet p0 = pset1<Packet>(0.2402264923f); + + const Packet C_hi = pset1<Packet>(0.6931471825f); + const Packet C_lo = pset1<Packet>(2.36836577e-08f); + const Packet one = pset1<Packet>(1.0f); + + // Evaluate P(x) in working precision. + // We evaluate even and odd parts of the polynomial separately + // to gain some instruction level parallelism. + Packet x2 = pmul(x,x); + Packet p_even = pmadd(p4, x2, p2); + Packet p_odd = pmadd(p3, x2, p1); + p_even = pmadd(p_even, x2, p0); + Packet p = pmadd(p_odd, x, p_even); + + // Evaluate the remaining terms of Q(x) with extra precision using + // double word arithmetic. + Packet p_hi, p_lo; + // x * p(x) + twoprod(p, x, p_hi, p_lo); + // C + x * p(x) + Packet q1_hi, q1_lo; + twosum(p_hi, p_lo, C_hi, C_lo, q1_hi, q1_lo); + // x * (C + x * p(x)) + Packet q2_hi, q2_lo; + twoprod(q1_hi, q1_lo, x, q2_hi, q2_lo); + // 1 + x * (C + x * p(x)) + Packet q3_hi, q3_lo; + // Since |q2_hi| <= sqrt(2)-1 < 1, we can use fast_twosum + // for adding it to unity here. + fast_twosum(one, q2_hi, q3_hi, q3_lo); + return padd(q3_hi, padd(q2_lo, q3_lo)); + } +}; + +// in [-0.5;0.5] with a relative accuracy of 1 ulp. +// The minimax polynomial used was calculated using the Sollya tool. +// See sollya.org. +template <> +struct fast_accurate_exp2<double> { + template <typename Packet> + EIGEN_STRONG_INLINE + Packet operator()(const Packet& x) { + // This function approximates exp2(x) by a degree 10 polynomial of the form + // Q(x) = 1 + x * (C + x * P(x)), where the degree 8 polynomial P(x) is evaluated in + // single precision, and the remaining steps are evaluated with extra precision using + // double word arithmetic. C is an extra precise constant stored as a double word. + // + // The polynomial coefficients were calculated using Sollya commands: + // > n = 11; + // > f = 2^x; + // > interval = [-0.5;0.5]; + // > p = fpminimax(f,n,[|1,DD,double...|],interval,relative,floating); + + const Packet p9 = pset1<Packet>(4.431642109085495276e-10); + const Packet p8 = pset1<Packet>(7.073829923303358410e-9); + const Packet p7 = pset1<Packet>(1.017822306737031311e-7); + const Packet p6 = pset1<Packet>(1.321543498017646657e-6); + const Packet p5 = pset1<Packet>(1.525273342728892877e-5); + const Packet p4 = pset1<Packet>(1.540353045780084423e-4); + const Packet p3 = pset1<Packet>(1.333355814685869807e-3); + const Packet p2 = pset1<Packet>(9.618129107593478832e-3); + const Packet p1 = pset1<Packet>(5.550410866481961247e-2); + const Packet p0 = pset1<Packet>(0.240226506959101332); + const Packet C_hi = pset1<Packet>(0.693147180559945286); + const Packet C_lo = pset1<Packet>(4.81927865669806721e-17); + const Packet one = pset1<Packet>(1.0); + + // Evaluate P(x) in working precision. + // We evaluate even and odd parts of the polynomial separately + // to gain some instruction level parallelism. + Packet x2 = pmul(x,x); + Packet p_even = pmadd(p8, x2, p6); + Packet p_odd = pmadd(p9, x2, p7); + p_even = pmadd(p_even, x2, p4); + p_odd = pmadd(p_odd, x2, p5); + p_even = pmadd(p_even, x2, p2); + p_odd = pmadd(p_odd, x2, p3); + p_even = pmadd(p_even, x2, p0); + p_odd = pmadd(p_odd, x2, p1); + Packet p = pmadd(p_odd, x, p_even); + + // Evaluate the remaining terms of Q(x) with extra precision using + // double word arithmetic. + Packet p_hi, p_lo; + // x * p(x) + twoprod(p, x, p_hi, p_lo); + // C + x * p(x) + Packet q1_hi, q1_lo; + twosum(p_hi, p_lo, C_hi, C_lo, q1_hi, q1_lo); + // x * (C + x * p(x)) + Packet q2_hi, q2_lo; + twoprod(q1_hi, q1_lo, x, q2_hi, q2_lo); + // 1 + x * (C + x * p(x)) + Packet q3_hi, q3_lo; + // Since |q2_hi| <= sqrt(2)-1 < 1, we can use fast_twosum + // for adding it to unity here. + fast_twosum(one, q2_hi, q3_hi, q3_lo); + return padd(q3_hi, padd(q2_lo, q3_lo)); + } +}; + +// This function implements the non-trivial case of pow(x,y) where x is +// positive and y is (possibly) non-integer. +// Formally, pow(x,y) = exp2(y * log2(x)), where exp2(x) is shorthand for 2^x. +// TODO(rmlarsen): We should probably add this as a packet up 'ppow', to make it +// easier to specialize or turn off for specific types and/or backends.x +template <typename Packet> +EIGEN_STRONG_INLINE Packet generic_pow_impl(const Packet& x, const Packet& y) { + typedef typename unpacket_traits<Packet>::type Scalar; + // Split x into exponent e_x and mantissa m_x. + Packet e_x; + Packet m_x = pfrexp(x, e_x); + + // Adjust m_x to lie in [1/sqrt(2):sqrt(2)] to minimize absolute error in log2(m_x). + EIGEN_CONSTEXPR Scalar sqrt_half = Scalar(0.70710678118654752440); + const Packet m_x_scale_mask = pcmp_lt(m_x, pset1<Packet>(sqrt_half)); + m_x = pselect(m_x_scale_mask, pmul(pset1<Packet>(Scalar(2)), m_x), m_x); + e_x = pselect(m_x_scale_mask, psub(e_x, pset1<Packet>(Scalar(1))), e_x); + + // Compute log2(m_x) with 6 extra bits of accuracy. + Packet rx_hi, rx_lo; + accurate_log2<Scalar>()(m_x, rx_hi, rx_lo); + + // Compute the two terms {y * e_x, y * r_x} in f = y * log2(x) with doubled + // precision using double word arithmetic. + Packet f1_hi, f1_lo, f2_hi, f2_lo; + twoprod(e_x, y, f1_hi, f1_lo); + twoprod(rx_hi, rx_lo, y, f2_hi, f2_lo); + // Sum the two terms in f using double word arithmetic. We know + // that |e_x| > |log2(m_x)|, except for the case where e_x==0. + // This means that we can use fast_twosum(f1,f2). + // In the case e_x == 0, e_x * y = f1 = 0, so we don't lose any + // accuracy by violating the assumption of fast_twosum, because + // it's a no-op. + Packet f_hi, f_lo; + fast_twosum(f1_hi, f1_lo, f2_hi, f2_lo, f_hi, f_lo); + + // Split f into integer and fractional parts. + Packet n_z, r_z; + absolute_split(f_hi, n_z, r_z); + r_z = padd(r_z, f_lo); + Packet n_r; + absolute_split(r_z, n_r, r_z); + n_z = padd(n_z, n_r); + + // We now have an accurate split of f = n_z + r_z and can compute + // x^y = 2**{n_z + r_z) = exp2(r_z) * 2**{n_z}. + // Since r_z is in [-0.5;0.5], we compute the first factor to high accuracy + // using a specialized algorithm. Multiplication by the second factor can + // be done exactly using pldexp(), since it is an integer power of 2. + const Packet e_r = fast_accurate_exp2<Scalar>()(r_z); + return pldexp(e_r, n_z); +} + +// Generic implementation of pow(x,y). +template<typename Packet> +EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS +EIGEN_UNUSED +Packet generic_pow(const Packet& x, const Packet& y) { + typedef typename unpacket_traits<Packet>::type Scalar; + + const Packet cst_pos_inf = pset1<Packet>(NumTraits<Scalar>::infinity()); + const Packet cst_zero = pset1<Packet>(Scalar(0)); + const Packet cst_one = pset1<Packet>(Scalar(1)); + const Packet cst_nan = pset1<Packet>(NumTraits<Scalar>::quiet_NaN()); + + const Packet abs_x = pabs(x); + // Predicates for sign and magnitude of x. + const Packet x_is_zero = pcmp_eq(x, cst_zero); + const Packet x_is_neg = pcmp_lt(x, cst_zero); + const Packet abs_x_is_inf = pcmp_eq(abs_x, cst_pos_inf); + const Packet abs_x_is_one = pcmp_eq(abs_x, cst_one); + const Packet abs_x_is_gt_one = pcmp_lt(cst_one, abs_x); + const Packet abs_x_is_lt_one = pcmp_lt(abs_x, cst_one); + const Packet x_is_one = pandnot(abs_x_is_one, x_is_neg); + const Packet x_is_neg_one = pand(abs_x_is_one, x_is_neg); + const Packet x_is_nan = pandnot(ptrue(x), pcmp_eq(x, x)); + + // Predicates for sign and magnitude of y. + const Packet y_is_one = pcmp_eq(y, cst_one); + const Packet y_is_zero = pcmp_eq(y, cst_zero); + const Packet y_is_neg = pcmp_lt(y, cst_zero); + const Packet y_is_pos = pandnot(ptrue(y), por(y_is_zero, y_is_neg)); + const Packet y_is_nan = pandnot(ptrue(y), pcmp_eq(y, y)); + const Packet abs_y_is_inf = pcmp_eq(pabs(y), cst_pos_inf); + EIGEN_CONSTEXPR Scalar huge_exponent = + (NumTraits<Scalar>::max_exponent() * Scalar(EIGEN_LN2)) / + NumTraits<Scalar>::epsilon(); + const Packet abs_y_is_huge = pcmp_le(pset1<Packet>(huge_exponent), pabs(y)); + + // Predicates for whether y is integer and/or even. + const Packet y_is_int = pcmp_eq(pfloor(y), y); + const Packet y_div_2 = pmul(y, pset1<Packet>(Scalar(0.5))); + const Packet y_is_even = pcmp_eq(pround(y_div_2), y_div_2); + + // Predicates encoding special cases for the value of pow(x,y) + const Packet invalid_negative_x = pandnot(pandnot(pandnot(x_is_neg, abs_x_is_inf), + y_is_int), + abs_y_is_inf); + const Packet pow_is_one = por(por(x_is_one, y_is_zero), + pand(x_is_neg_one, + por(abs_y_is_inf, pandnot(y_is_even, invalid_negative_x)))); + const Packet pow_is_nan = por(invalid_negative_x, por(x_is_nan, y_is_nan)); + const Packet pow_is_zero = por(por(por(pand(x_is_zero, y_is_pos), + pand(abs_x_is_inf, y_is_neg)), + pand(pand(abs_x_is_lt_one, abs_y_is_huge), + y_is_pos)), + pand(pand(abs_x_is_gt_one, abs_y_is_huge), + y_is_neg)); + const Packet pow_is_inf = por(por(por(pand(x_is_zero, y_is_neg), + pand(abs_x_is_inf, y_is_pos)), + pand(pand(abs_x_is_lt_one, abs_y_is_huge), + y_is_neg)), + pand(pand(abs_x_is_gt_one, abs_y_is_huge), + y_is_pos)); + + // General computation of pow(x,y) for positive x or negative x and integer y. + const Packet negate_pow_abs = pandnot(x_is_neg, y_is_even); + const Packet pow_abs = generic_pow_impl(abs_x, y); + return pselect(y_is_one, x, + pselect(pow_is_one, cst_one, + pselect(pow_is_nan, cst_nan, + pselect(pow_is_inf, cst_pos_inf, + pselect(pow_is_zero, cst_zero, + pselect(negate_pow_abs, pnegate(pow_abs), pow_abs)))))); +} + + + +/* polevl (modified for Eigen) + * + * Evaluate polynomial + * + * + * + * SYNOPSIS: + * + * int N; + * Scalar x, y, coef[N+1]; + * + * y = polevl<decltype(x), N>( x, coef); + * + * + * + * DESCRIPTION: + * + * Evaluates polynomial of degree N: + * + * 2 N + * y = C + C x + C x +...+ C x + * 0 1 2 N + * + * Coefficients are stored in reverse order: + * + * coef[0] = C , ..., coef[N] = C . + * N 0 + * + * The function p1evl() assumes that coef[N] = 1.0 and is + * omitted from the array. Its calling arguments are + * otherwise the same as polevl(). + * + * + * The Eigen implementation is templatized. For best speed, store + * coef as a const array (constexpr), e.g. + * + * const double coef[] = {1.0, 2.0, 3.0, ...}; + * + */ +template <typename Packet, int N> +struct ppolevl { + static EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE Packet run(const Packet& x, const typename unpacket_traits<Packet>::type coeff[]) { + EIGEN_STATIC_ASSERT((N > 0), YOU_MADE_A_PROGRAMMING_MISTAKE); + return pmadd(ppolevl<Packet, N-1>::run(x, coeff), x, pset1<Packet>(coeff[N])); + } +}; + +template <typename Packet> +struct ppolevl<Packet, 0> { + static EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE Packet run(const Packet& x, const typename unpacket_traits<Packet>::type coeff[]) { + EIGEN_UNUSED_VARIABLE(x); + return pset1<Packet>(coeff[0]); + } +}; + +/* chbevl (modified for Eigen) + * + * Evaluate Chebyshev series + * + * + * + * SYNOPSIS: + * + * int N; + * Scalar x, y, coef[N], chebevl(); + * + * y = chbevl( x, coef, N ); + * + * + * + * DESCRIPTION: + * + * Evaluates the series + * + * N-1 + * - ' + * y = > coef[i] T (x/2) + * - i + * i=0 + * + * of Chebyshev polynomials Ti at argument x/2. + * + * Coefficients are stored in reverse order, i.e. the zero + * order term is last in the array. Note N is the number of + * coefficients, not the order. + * + * If coefficients are for the interval a to b, x must + * have been transformed to x -> 2(2x - b - a)/(b-a) before + * entering the routine. This maps x from (a, b) to (-1, 1), + * over which the Chebyshev polynomials are defined. + * + * If the coefficients are for the inverted interval, in + * which (a, b) is mapped to (1/b, 1/a), the transformation + * required is x -> 2(2ab/x - b - a)/(b-a). If b is infinity, + * this becomes x -> 4a/x - 1. + * + * + * + * SPEED: + * + * Taking advantage of the recurrence properties of the + * Chebyshev polynomials, the routine requires one more + * addition per loop than evaluating a nested polynomial of + * the same degree. + * + */ + +template <typename Packet, int N> +struct pchebevl { + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE Packet run(Packet x, const typename unpacket_traits<Packet>::type coef[]) { + typedef typename unpacket_traits<Packet>::type Scalar; + Packet b0 = pset1<Packet>(coef[0]); + Packet b1 = pset1<Packet>(static_cast<Scalar>(0.f)); + Packet b2; + + for (int i = 1; i < N; i++) { + b2 = b1; + b1 = b0; + b0 = psub(pmadd(x, b1, pset1<Packet>(coef[i])), b2); + } + + return pmul(pset1<Packet>(static_cast<Scalar>(0.5f)), psub(b0, b2)); + } +}; + +} // end namespace internal +} // end namespace Eigen + +#endif // EIGEN_ARCH_GENERIC_PACKET_MATH_FUNCTIONS_H |