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/* Helper for single-precision AdvSIMD 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_V_EXPF_INLINE_H
#define AARCH64_FPU_V_EXPF_INLINE_H
#include "v_math.h"
struct v_expf_data
{
float32x4_t poly[5];
float32x4_t shift, invln2_and_ln2;
};
/* maxerr: 1.45358 +0.5 ulp. */
#define V_EXPF_DATA \
{ \
.poly = { V4 (0x1.0e4020p-7f), V4 (0x1.573e2ep-5f), V4 (0x1.555e66p-3f), \
V4 (0x1.fffdb6p-2f), V4 (0x1.ffffecp-1f) }, \
.shift = V4 (0x1.8p23f), \
.invln2_and_ln2 = { 0x1.715476p+0f, 0x1.62e4p-1f, 0x1.7f7d1cp-20f, 0 }, \
}
#define ExponentBias v_u32 (0x3f800000) /* asuint(1.0f). */
#define C(i) d->poly[i]
static inline float32x4_t
v_expf_inline (float32x4_t x, const struct v_expf_data *d)
{
/* Helper routine for calculating exp(x).
Copied from v_expf.c, with all special-case handling removed - the
calling routine should handle special values if required. */
/* 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]. */
float32x4_t n, r, z;
z = vfmaq_laneq_f32 (d->shift, x, d->invln2_and_ln2, 0);
n = vsubq_f32 (z, d->shift);
r = vfmsq_laneq_f32 (x, n, d->invln2_and_ln2, 1);
r = vfmsq_laneq_f32 (r, n, d->invln2_and_ln2, 2);
uint32x4_t e = vshlq_n_u32 (vreinterpretq_u32_f32 (z), 23);
float32x4_t scale = vreinterpretq_f32_u32 (vaddq_u32 (e, ExponentBias));
/* Custom order-4 Estrin avoids building high order monomial. */
float32x4_t r2 = vmulq_f32 (r, r);
float32x4_t p, q, poly;
p = vfmaq_f32 (C (1), C (0), r);
q = vfmaq_f32 (C (3), C (2), r);
q = vfmaq_f32 (q, p, r2);
p = vmulq_f32 (C (4), r);
poly = vfmaq_f32 (p, q, r2);
return vfmaq_f32 (scale, poly, scale);
}
#endif
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