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76 lines
2.9 KiB
C
76 lines
2.9 KiB
C
/* SVE helper for single-precision routines which depend on exp
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Copyright (C) 2024 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#ifndef AARCH64_FPU_SV_EXPF_INLINE_H
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#define AARCH64_FPU_SV_EXPF_INLINE_H
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#include "sv_math.h"
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struct sv_expf_data
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{
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float poly[5];
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float inv_ln2, ln2_hi, ln2_lo, shift;
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};
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/* Coefficients copied from the polynomial in AdvSIMD variant, reversed for
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compatibility with polynomial helpers. Shift is 1.5*2^17 + 127. */
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#define SV_EXPF_DATA \
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{ \
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.poly = { 0x1.ffffecp-1f, 0x1.fffdb6p-2f, 0x1.555e66p-3f, 0x1.573e2ep-5f, \
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0x1.0e4020p-7f }, \
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\
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.inv_ln2 = 0x1.715476p+0f, .ln2_hi = 0x1.62e4p-1f, \
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.ln2_lo = 0x1.7f7d1cp-20f, .shift = 0x1.803f8p17f, \
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}
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#define C(i) sv_f32 (d->poly[i])
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static inline svfloat32_t
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expf_inline (svfloat32_t x, const svbool_t pg, const struct sv_expf_data *d)
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{
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/* exp(x) = 2^n (1 + poly(r)), with 1 + poly(r) in [1/sqrt(2),sqrt(2)]
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x = ln2*n + r, with r in [-ln2/2, ln2/2]. */
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/* Load some constants in quad-word chunks to minimise memory access. */
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svfloat32_t c4_invln2_and_ln2 = svld1rq (svptrue_b32 (), &d->poly[4]);
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/* n = round(x/(ln2/N)). */
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svfloat32_t z = svmla_lane (sv_f32 (d->shift), x, c4_invln2_and_ln2, 1);
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svfloat32_t n = svsub_x (pg, z, d->shift);
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/* r = x - n*ln2/N. */
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svfloat32_t r = svmls_lane (x, n, c4_invln2_and_ln2, 2);
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r = svmls_lane (r, n, c4_invln2_and_ln2, 3);
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/* scale = 2^(n/N). */
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svfloat32_t scale = svexpa (svreinterpret_u32_f32 (z));
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/* y = exp(r) - 1 ~= r + C0 r^2 + C1 r^3 + C2 r^4 + C3 r^5 + C4 r^6. */
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svfloat32_t p12 = svmla_x (pg, C (1), C (2), r);
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svfloat32_t p34 = svmla_lane (C (3), r, c4_invln2_and_ln2, 0);
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svfloat32_t r2 = svmul_f32_x (pg, r, r);
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svfloat32_t p14 = svmla_x (pg, p12, p34, r2);
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svfloat32_t p0 = svmul_f32_x (pg, r, C (0));
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svfloat32_t poly = svmla_x (pg, p0, r2, p14);
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return svmla_x (pg, scale, scale, poly);
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}
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#endif
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