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Diffstat (limited to 'sysdeps/aarch64/fpu/v_expm1f_inline.h')
| -rw-r--r-- | sysdeps/aarch64/fpu/v_expm1f_inline.h | 73 |
1 files changed, 73 insertions, 0 deletions
diff --git a/sysdeps/aarch64/fpu/v_expm1f_inline.h b/sysdeps/aarch64/fpu/v_expm1f_inline.h new file mode 100644 index 0000000000..337ccfbfab --- /dev/null +++ b/sysdeps/aarch64/fpu/v_expm1f_inline.h @@ -0,0 +1,73 @@ +/* Single-precision inline helper for vector (Advanced SIMD) expm1 function + + 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_V_EXPM1F_INLINE_H +#define AARCH64_FPU_V_EXPM1F_INLINE_H + +#include "v_math.h" +#include "poly_advsimd_f32.h" + +struct v_expm1f_data +{ + float32x4_t poly[5]; + float32x4_t invln2_and_ln2, shift; + int32x4_t exponent_bias; +}; + +/* Coefficients generated using fpminimax with degree=5 in [-log(2)/2, + log(2)/2]. Exponent bias is asuint(1.0f). + invln2_and_ln2 Stores constants: invln2, ln2_lo, ln2_hi, 0. */ +#define V_EXPM1F_DATA \ + { \ + .poly = { V4 (0x1.fffffep-2), V4 (0x1.5554aep-3), V4 (0x1.555736p-5), \ + V4 (0x1.12287cp-7), V4 (0x1.6b55a2p-10) }, \ + .shift = V4 (0x1.8p23f), .exponent_bias = V4 (0x3f800000), \ + .invln2_and_ln2 = { 0x1.715476p+0f, 0x1.62e4p-1f, 0x1.7f7d1cp-20f, 0 }, \ + } + +static inline float32x4_t +expm1f_inline (float32x4_t x, const struct v_expm1f_data *d) +{ + /* Helper routine for calculating exp(x) - 1. + Copied from v_expm1f_1u6.c, with all special-case handling removed - the + calling routine should handle special values if required. */ + + /* Reduce argument: f in [-ln2/2, ln2/2], i is exact. */ + float32x4_t j = vsubq_f32 ( + vfmaq_laneq_f32 (d->shift, x, d->invln2_and_ln2, 0), d->shift); + int32x4_t i = vcvtq_s32_f32 (j); + float32x4_t f = vfmsq_laneq_f32 (x, j, d->invln2_and_ln2, 1); + f = vfmsq_laneq_f32 (f, j, d->invln2_and_ln2, 2); + + /* Approximate expm1(f) with polynomial P, expm1(f) ~= f + f^2 * P(f). + Uses Estrin scheme, where the main _ZGVnN4v_expm1f routine uses + Horner. */ + float32x4_t f2 = vmulq_f32 (f, f); + float32x4_t f4 = vmulq_f32 (f2, f2); + float32x4_t p = v_estrin_4_f32 (f, f2, f4, d->poly); + p = vfmaq_f32 (f, f2, p); + + /* t = 2^i. */ + int32x4_t u = vaddq_s32 (vshlq_n_s32 (i, 23), d->exponent_bias); + float32x4_t t = vreinterpretq_f32_s32 (u); + /* expm1(x) ~= p * t + (t - 1). */ + return vfmaq_f32 (vsubq_f32 (t, v_f32 (1.0f)), p, t); +} + +#endif |