diff options
Diffstat (limited to 'sysdeps/aarch64/fpu/sv_expf_inline.h')
| -rw-r--r-- | sysdeps/aarch64/fpu/sv_expf_inline.h | 75 |
1 files changed, 75 insertions, 0 deletions
diff --git a/sysdeps/aarch64/fpu/sv_expf_inline.h b/sysdeps/aarch64/fpu/sv_expf_inline.h new file mode 100644 index 0000000000..23963b5f8e --- /dev/null +++ b/sysdeps/aarch64/fpu/sv_expf_inline.h @@ -0,0 +1,75 @@ +/* SVE helper for single-precision routines which depend on exp + + Copyright (C) 2024 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/>. */ + +#ifndef AARCH64_FPU_SV_EXPF_INLINE_H +#define AARCH64_FPU_SV_EXPF_INLINE_H + +#include "sv_math.h" + +struct sv_expf_data +{ + float poly[5]; + float inv_ln2, ln2_hi, ln2_lo, shift; +}; + +/* Coefficients copied from the polynomial in AdvSIMD variant, reversed for + compatibility with polynomial helpers. Shift is 1.5*2^17 + 127. */ +#define SV_EXPF_DATA \ + { \ + .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, .shift = 0x1.803f8p17f, \ + } + +#define C(i) sv_f32 (d->poly[i]) + +static inline svfloat32_t +expf_inline (svfloat32_t x, const svbool_t pg, const struct sv_expf_data *d) +{ + /* 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. */ + svfloat32_t c4_invln2_and_ln2 = svld1rq (svptrue_b32 (), &d->poly[4]); + + /* n = round(x/(ln2/N)). */ + svfloat32_t z = svmla_lane (sv_f32 (d->shift), x, c4_invln2_and_ln2, 1); + svfloat32_t n = svsub_x (pg, z, d->shift); + + /* r = x - n*ln2/N. */ + svfloat32_t r = svmls_lane (x, n, c4_invln2_and_ln2, 2); + r = svmls_lane (r, n, c4_invln2_and_ln2, 3); + + /* scale = 2^(n/N). */ + svfloat32_t scale = svexpa (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_x (pg, C (1), C (2), r); + svfloat32_t p34 = svmla_lane (C (3), r, c4_invln2_and_ln2, 0); + svfloat32_t r2 = svmul_f32_x (pg, r, r); + svfloat32_t p14 = svmla_x (pg, p12, p34, r2); + svfloat32_t p0 = svmul_f32_x (pg, r, C (0)); + svfloat32_t poly = svmla_x (pg, p0, r2, p14); + + return svmla_x (pg, scale, scale, poly); +} + +#endif |