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Diffstat (limited to 'pl/math/sv_log_2u5.c')
| -rw-r--r-- | pl/math/sv_log_2u5.c | 85 |
1 files changed, 85 insertions, 0 deletions
diff --git a/pl/math/sv_log_2u5.c b/pl/math/sv_log_2u5.c new file mode 100644 index 0000000..7f06fd3 --- /dev/null +++ b/pl/math/sv_log_2u5.c @@ -0,0 +1,85 @@ +/* + * Double-precision SVE log(x) function. + * + * Copyright (c) 2020-2023, Arm Limited. + * SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception + */ + +#include "sv_math.h" +#include "pl_sig.h" +#include "pl_test.h" + +#if SV_SUPPORTED + +#define A(i) __sv_log_data.poly[i] +#define Ln2 (0x1.62e42fefa39efp-1) +#define N (1 << SV_LOG_TABLE_BITS) +#define OFF (0x3fe6900900000000) + +double +optr_aor_log_f64 (double); + +static NOINLINE sv_f64_t +__sv_log_specialcase (sv_f64_t x, sv_f64_t y, svbool_t cmp) +{ + return sv_call_f64 (optr_aor_log_f64, x, y, cmp); +} + +/* SVE port of Neon log algorithm from math/. + Maximum measured error is 2.17 ulp: + __sv_log(0x1.a6129884398a3p+0) got 0x1.ffffff1cca043p-2 + want 0x1.ffffff1cca045p-2. */ +sv_f64_t +__sv_log_x (sv_f64_t x, const svbool_t pg) +{ + sv_u64_t ix = sv_as_u64_f64 (x); + sv_u64_t top = svlsr_n_u64_x (pg, ix, 48); + svbool_t cmp = svcmpge_u64 (pg, svsub_n_u64_x (pg, top, 0x0010), + sv_u64 (0x7ff0 - 0x0010)); + + /* x = 2^k z; where z is in range [OFF,2*OFF) and exact. + The range is split into N subintervals. + The ith subinterval contains z and c is near its center. */ + sv_u64_t tmp = svsub_n_u64_x (pg, ix, OFF); + /* Equivalent to (tmp >> (52 - SV_LOG_TABLE_BITS)) % N, since N is a power + of 2. */ + sv_u64_t i + = svand_n_u64_x (pg, svlsr_n_u64_x (pg, tmp, (52 - SV_LOG_TABLE_BITS)), + N - 1); + sv_s64_t k + = svasr_n_s64_x (pg, sv_as_s64_u64 (tmp), 52); /* Arithmetic shift. */ + sv_u64_t iz = svsub_u64_x (pg, ix, svand_n_u64_x (pg, tmp, 0xfffULL << 52)); + sv_f64_t z = sv_as_f64_u64 (iz); + /* Lookup in 2 global lists (length N). */ + sv_f64_t invc = sv_lookup_f64_x (pg, __sv_log_data.invc, i); + sv_f64_t logc = sv_lookup_f64_x (pg, __sv_log_data.logc, i); + + /* log(x) = log1p(z/c-1) + log(c) + k*Ln2. */ + sv_f64_t r = sv_fma_f64_x (pg, z, invc, sv_f64 (-1.0)); + sv_f64_t kd = sv_to_f64_s64_x (pg, k); + /* hi = r + log(c) + k*Ln2. */ + sv_f64_t hi = sv_fma_n_f64_x (pg, Ln2, kd, svadd_f64_x (pg, logc, r)); + /* y = r2*(A0 + r*A1 + r2*(A2 + r*A3 + r2*A4)) + hi. */ + sv_f64_t r2 = svmul_f64_x (pg, r, r); + sv_f64_t y = sv_fma_n_f64_x (pg, A (3), r, sv_f64 (A (2))); + sv_f64_t p = sv_fma_n_f64_x (pg, A (1), r, sv_f64 (A (0))); + y = sv_fma_n_f64_x (pg, A (4), r2, y); + y = sv_fma_f64_x (pg, y, r2, p); + y = sv_fma_f64_x (pg, y, r2, hi); + + if (unlikely (svptest_any (pg, cmp))) + return __sv_log_specialcase (x, y, cmp); + return y; +} + +PL_ALIAS (__sv_log_x, _ZGVsMxv_log) + +PL_SIG (SV, D, 1, log, 0.01, 11.1) +PL_TEST_ULP (__sv_log, 1.68) +PL_TEST_INTERVAL (__sv_log, -0.0, -0x1p126, 100) +PL_TEST_INTERVAL (__sv_log, 0x1p-149, 0x1p-126, 4000) +PL_TEST_INTERVAL (__sv_log, 0x1p-126, 0x1p-23, 50000) +PL_TEST_INTERVAL (__sv_log, 0x1p-23, 1.0, 50000) +PL_TEST_INTERVAL (__sv_log, 1.0, 100, 50000) +PL_TEST_INTERVAL (__sv_log, 100, inf, 50000) +#endif // SV_SUPPORTED |