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/* 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
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