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Diffstat (limited to 'pl/math/atanf_common.h')
-rw-r--r-- | pl/math/atanf_common.h | 51 |
1 files changed, 51 insertions, 0 deletions
diff --git a/pl/math/atanf_common.h b/pl/math/atanf_common.h new file mode 100644 index 0000000..37ca76d --- /dev/null +++ b/pl/math/atanf_common.h @@ -0,0 +1,51 @@ +/* + * Single-precision polynomial evaluation function for scalar and vector + * atan(x) and atan2(y,x). + * + * Copyright (c) 2021-2023, Arm Limited. + * SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception + */ + +#ifndef PL_MATH_ATANF_COMMON_H +#define PL_MATH_ATANF_COMMON_H + +#include "math_config.h" +#include "estrinf.h" + +#if V_SUPPORTED + +#include "v_math.h" + +#define FLT_T v_f32_t +#define P(i) v_f32 (__atanf_poly_data.poly[i]) + +#else + +#define FLT_T float +#define P(i) __atanf_poly_data.poly[i] + +#endif + +/* Polynomial used in fast atanf(x) and atan2f(y,x) implementations + The order 7 polynomial P approximates (atan(sqrt(x))-sqrt(x))/x^(3/2). */ +static inline FLT_T +eval_poly (FLT_T z, FLT_T az, FLT_T shift) +{ + /* Use 2-level Estrin scheme for P(z^2) with deg(P)=7. However, + a standard implementation using z8 creates spurious underflow + in the very last fma (when z^8 is small enough). + Therefore, we split the last fma into a mul and and an fma. + Horner and single-level Estrin have higher errors that exceed + threshold. */ + FLT_T z2 = z * z; + FLT_T z4 = z2 * z2; + + /* Then assemble polynomial. */ + FLT_T y = FMA (z4, z4 * ESTRIN_3_ (z2, z4, P, 4), ESTRIN_3 (z2, z4, P)); + + /* Finalize: + y = shift + z * P(z^2). */ + return FMA (y, z2 * az, az) + shift; +} + +#endif // PL_MATH_ATANF_COMMON_H |