diff options
Diffstat (limited to 'sysdeps/aarch64/fpu/log_sve.c')
| -rw-r--r-- | sysdeps/aarch64/fpu/log_sve.c | 80 |
1 files changed, 80 insertions, 0 deletions
diff --git a/sysdeps/aarch64/fpu/log_sve.c b/sysdeps/aarch64/fpu/log_sve.c new file mode 100644 index 0000000000..93c4f1c018 --- /dev/null +++ b/sysdeps/aarch64/fpu/log_sve.c @@ -0,0 +1,80 @@ +/* Double-precision vector (SVE) log function. + + Copyright (C) 2023 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + <https://www.gnu.org/licenses/>. */ + +#include "sv_math.h" + +#define P(i) sv_f64 (__v_log_data.poly[i]) +#define N (1 << V_LOG_TABLE_BITS) +#define Off (0x3fe6900900000000) +#define MaxTop (0x7ff) +#define MinTop (0x001) +#define ThreshTop (0x7fe) /* MaxTop - MinTop. */ + +static svfloat64_t NOINLINE +special_case (svfloat64_t x, svfloat64_t y, svbool_t cmp) +{ + return sv_call_f64 (log, x, y, cmp); +} + +/* SVE port of AdvSIMD log algorithm. + Maximum measured error is 2.17 ulp: + SV_NAME_D1 (log)(0x1.a6129884398a3p+0) got 0x1.ffffff1cca043p-2 + want 0x1.ffffff1cca045p-2. */ +svfloat64_t SV_NAME_D1 (log) (svfloat64_t x, const svbool_t pg) +{ + svuint64_t ix = svreinterpret_u64_f64 (x); + svuint64_t top = svlsr_n_u64_x (pg, ix, 52); + svbool_t cmp + = svcmpge_u64 (pg, svsub_n_u64_x (pg, top, MinTop), sv_u64 (ThreshTop)); + + /* 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. */ + svuint64_t tmp = svsub_n_u64_x (pg, ix, Off); + /* Equivalent to (tmp >> (52 - V_LOG_TABLE_BITS)) % N, since N is a power + of 2. */ + svuint64_t i = svand_n_u64_x ( + pg, svlsr_n_u64_x (pg, tmp, (52 - V_LOG_TABLE_BITS)), N - 1); + svint64_t k = svasr_n_s64_x (pg, svreinterpret_s64_u64 (tmp), + 52); /* Arithmetic shift. */ + svuint64_t iz + = svsub_u64_x (pg, ix, svand_n_u64_x (pg, tmp, 0xfffULL << 52)); + svfloat64_t z = svreinterpret_f64_u64 (iz); + /* Lookup in 2 global lists (length N). */ + svfloat64_t invc = svld1_gather_u64index_f64 (pg, __v_log_data.invc, i); + svfloat64_t logc = svld1_gather_u64index_f64 (pg, __v_log_data.logc, i); + + /* log(x) = log1p(z/c-1) + log(c) + k*Ln2. */ + svfloat64_t r = svmad_n_f64_x (pg, invc, z, -1); + svfloat64_t kd = svcvt_f64_s64_x (pg, k); + /* hi = r + log(c) + k*Ln2. */ + svfloat64_t hi + = svmla_n_f64_x (pg, svadd_f64_x (pg, logc, r), kd, __v_log_data.ln2); + /* y = r2*(A0 + r*A1 + r2*(A2 + r*A3 + r2*A4)) + hi. */ + svfloat64_t r2 = svmul_f64_x (pg, r, r); + svfloat64_t y = svmla_f64_x (pg, P (2), r, P (3)); + svfloat64_t p = svmla_f64_x (pg, P (0), r, P (1)); + y = svmla_f64_x (pg, y, r2, P (4)); + y = svmla_f64_x (pg, p, r2, y); + y = svmla_f64_x (pg, hi, r2, y); + + if (__glibc_unlikely (svptest_any (pg, cmp))) + return special_case (x, y, cmp); + return y; +} |