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Diffstat (limited to 'sysdeps/aarch64/fpu/v_log1pf_inline.h')
| -rw-r--r-- | sysdeps/aarch64/fpu/v_log1pf_inline.h | 78 |
1 files changed, 78 insertions, 0 deletions
diff --git a/sysdeps/aarch64/fpu/v_log1pf_inline.h b/sysdeps/aarch64/fpu/v_log1pf_inline.h new file mode 100644 index 0000000000..643a6cdcfc --- /dev/null +++ b/sysdeps/aarch64/fpu/v_log1pf_inline.h @@ -0,0 +1,78 @@ +/* Helper for single-precision Advanced SIMD routines which depend on log1p + + 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_LOG1PF_INLINE_H +#define AARCH64_FPU_V_LOG1PF_INLINE_H + +#include "v_math.h" +#include "poly_advsimd_f32.h" + +struct v_log1pf_data +{ + float32x4_t poly[8], ln2; + uint32x4_t four; + int32x4_t three_quarters; +}; + +/* Polynomial generated using FPMinimax in [-0.25, 0.5]. First two coefficients + (1, -0.5) are not stored as they can be generated more efficiently. */ +#define V_LOG1PF_CONSTANTS_TABLE \ + { \ + .poly \ + = { V4 (0x1.5555aap-2f), V4 (-0x1.000038p-2f), V4 (0x1.99675cp-3f), \ + V4 (-0x1.54ef78p-3f), V4 (0x1.28a1f4p-3f), V4 (-0x1.0da91p-3f), \ + V4 (0x1.abcb6p-4f), V4 (-0x1.6f0d5ep-5f) }, \ + .ln2 = V4 (0x1.62e43p-1f), .four = V4 (0x40800000), \ + .three_quarters = V4 (0x3f400000) \ + } + +static inline float32x4_t +eval_poly (float32x4_t m, const float32x4_t *c) +{ + /* Approximate log(1+m) on [-0.25, 0.5] using pairwise Horner (main routine + uses split Estrin, but this way reduces register pressure in the calling + routine). */ + float32x4_t q = vfmaq_f32 (v_f32 (-0.5), m, c[0]); + float32x4_t m2 = vmulq_f32 (m, m); + q = vfmaq_f32 (m, m2, q); + float32x4_t p = v_pw_horner_6_f32 (m, m2, c + 1); + p = vmulq_f32 (m2, p); + return vfmaq_f32 (q, m2, p); +} + +static inline float32x4_t +log1pf_inline (float32x4_t x, const struct v_log1pf_data d) +{ + /* Helper for calculating log(x + 1). Copied from log1pf_2u1.c, with no + special-case handling. See that file for details of the algorithm. */ + float32x4_t m = vaddq_f32 (x, v_f32 (1.0f)); + int32x4_t k + = vandq_s32 (vsubq_s32 (vreinterpretq_s32_f32 (m), d.three_quarters), + v_s32 (0xff800000)); + uint32x4_t ku = vreinterpretq_u32_s32 (k); + float32x4_t s = vreinterpretq_f32_u32 (vsubq_u32 (d.four, ku)); + float32x4_t m_scale + = vreinterpretq_f32_u32 (vsubq_u32 (vreinterpretq_u32_f32 (x), ku)); + m_scale = vaddq_f32 (m_scale, vfmaq_f32 (v_f32 (-1.0f), v_f32 (0.25f), s)); + float32x4_t p = eval_poly (m_scale, d.poly); + float32x4_t scale_back = vmulq_f32 (vcvtq_f32_s32 (k), v_f32 (0x1.0p-23f)); + return vfmaq_f32 (p, scale_back, d.ln2); +} + +#endif |