diff options
Diffstat (limited to 'sysdeps/aarch64/fpu/expf_sve.c')
| -rw-r--r-- | sysdeps/aarch64/fpu/expf_sve.c | 90 |
1 files changed, 90 insertions, 0 deletions
diff --git a/sysdeps/aarch64/fpu/expf_sve.c b/sysdeps/aarch64/fpu/expf_sve.c new file mode 100644 index 0000000000..03f2e086ed --- /dev/null +++ b/sysdeps/aarch64/fpu/expf_sve.c @@ -0,0 +1,90 @@ +/* Single-precision vector (SVE) exp 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" + +static const struct data +{ + float poly[5]; + float inv_ln2, ln2_hi, ln2_lo, shift, thres; +} data = { + /* Coefficients copied from the polynomial in AdvSIMD variant, reversed for + compatibility with polynomial helpers. */ + .poly = { 0x1.ffffecp-1f, 0x1.fffdb6p-2f, 0x1.555e66p-3f, 0x1.573e2ep-5f, + 0x1.0e4020p-7f }, + .inv_ln2 = 0x1.715476p+0f, + .ln2_hi = 0x1.62e4p-1f, + .ln2_lo = 0x1.7f7d1cp-20f, + /* 1.5*2^17 + 127. */ + .shift = 0x1.903f8p17f, + /* Roughly 87.3. For x < -Thres, the result is subnormal and not handled + correctly by FEXPA. */ + .thres = 0x1.5d5e2ap+6f, +}; + +#define C(i) sv_f32 (d->poly[i]) +#define ExponentBias 0x3f800000 + +static svfloat32_t NOINLINE +special_case (svfloat32_t x, svfloat32_t y, svbool_t special) +{ + return sv_call_f32 (expf, x, y, special); +} + +/* Optimised single-precision SVE exp function. + Worst-case error is 1.04 ulp: + SV_NAME_F1 (exp)(0x1.a8eda4p+1) got 0x1.ba74bcp+4 + want 0x1.ba74bap+4. */ +svfloat32_t SV_NAME_F1 (exp) (svfloat32_t x, const svbool_t pg) +{ + const struct data *d = ptr_barrier (&data); + + /* exp(x) = 2^n (1 + poly(r)), with 1 + poly(r) in [1/sqrt(2),sqrt(2)] + x = ln2*n + r, with r in [-ln2/2, ln2/2]. */ + + /* Load some constants in quad-word chunks to minimise memory access (last + lane is wasted). */ + svfloat32_t invln2_and_ln2 = svld1rq_f32 (svptrue_b32 (), &d->inv_ln2); + + /* n = round(x/(ln2/N)). */ + svfloat32_t z = svmla_lane_f32 (sv_f32 (d->shift), x, invln2_and_ln2, 0); + svfloat32_t n = svsub_n_f32_x (pg, z, d->shift); + + /* r = x - n*ln2/N. */ + svfloat32_t r = svmls_lane_f32 (x, n, invln2_and_ln2, 1); + r = svmls_lane_f32 (r, n, invln2_and_ln2, 2); + +/* scale = 2^(n/N). */ + svbool_t is_special_case = svacgt_n_f32 (pg, x, d->thres); + svfloat32_t scale = svexpa_f32 (svreinterpret_u32_f32 (z)); + + /* y = exp(r) - 1 ~= r + C0 r^2 + C1 r^3 + C2 r^4 + C3 r^5 + C4 r^6. */ + svfloat32_t p12 = svmla_f32_x (pg, C (1), C (2), r); + svfloat32_t p34 = svmla_f32_x (pg, C (3), C (4), r); + svfloat32_t r2 = svmul_f32_x (pg, r, r); + svfloat32_t p14 = svmla_f32_x (pg, p12, p34, r2); + svfloat32_t p0 = svmul_f32_x (pg, r, C (0)); + svfloat32_t poly = svmla_f32_x (pg, p0, r2, p14); + + if (__glibc_unlikely (svptest_any (pg, is_special_case))) + return special_case (x, svmla_f32_x (pg, scale, scale, poly), + is_special_case); + + return svmla_f32_x (pg, scale, scale, poly); +} |