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/* Single-precision vector (AdvSIMD) exp2 function
Copyright (C) 2023-2025 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/>. */
#include "v_math.h"
static const struct data
{
float32x4_t c1, c3;
uint32x4_t exponent_bias, special_offset, special_bias;
float32x4_t scale_thresh, special_bound;
float c0, c2, c4, zero;
} data = {
/* maxerr: 1.962 ulp. */
.c0 = 0x1.59977ap-10f,
.c1 = V4 (0x1.3ce9e4p-7f),
.c2 = 0x1.c6bd32p-5f,
.c3 = V4 (0x1.ebf9bcp-3f),
.c4 = 0x1.62e422p-1f,
.exponent_bias = V4 (0x3f800000),
.special_offset = V4 (0x82000000),
.special_bias = V4 (0x7f000000),
.special_bound = V4 (126.0f),
.scale_thresh = V4 (192.0f),
};
static float32x4_t VPCS_ATTR NOINLINE
special_case (float32x4_t poly, float32x4_t n, uint32x4_t e, uint32x4_t cmp1,
float32x4_t scale, const struct data *d)
{
/* 2^n may overflow, break it up into s1*s2. */
uint32x4_t b = vandq_u32 (vclezq_f32 (n), d->special_offset);
float32x4_t s1 = vreinterpretq_f32_u32 (vaddq_u32 (b, d->special_bias));
float32x4_t s2 = vreinterpretq_f32_u32 (vsubq_u32 (e, b));
uint32x4_t cmp2 = vcagtq_f32 (n, d->scale_thresh);
float32x4_t r2 = vmulq_f32 (s1, s1);
float32x4_t r1 = vmulq_f32 (vfmaq_f32 (s2, poly, s2), s1);
/* Similar to r1 but avoids double rounding in the subnormal range. */
float32x4_t r0 = vfmaq_f32 (scale, poly, scale);
float32x4_t r = vbslq_f32 (cmp1, r1, r0);
return vbslq_f32 (cmp2, r2, r);
}
float32x4_t VPCS_ATTR NOINLINE V_NAME_F1 (exp2) (float32x4_t x)
{
const struct data *d = ptr_barrier (&data);
/* exp2(x) = 2^n (1 + poly(r)), with 1 + poly(r) in [1/sqrt(2),sqrt(2)]
x = n + r, with r in [-1/2, 1/2]. */
float32x4_t n = vrndaq_f32 (x);
float32x4_t r = vsubq_f32 (x, n);
uint32x4_t e = vshlq_n_u32 (vreinterpretq_u32_s32 (vcvtaq_s32_f32 (x)), 23);
float32x4_t scale = vreinterpretq_f32_u32 (vaddq_u32 (e, d->exponent_bias));
uint32x4_t cmp = vcagtq_f32 (n, d->special_bound);
float32x4_t c024 = vld1q_f32 (&d->c0);
float32x4_t r2 = vmulq_f32 (r, r);
float32x4_t p = vfmaq_laneq_f32 (d->c1, r, c024, 0);
float32x4_t q = vfmaq_laneq_f32 (d->c3, r, c024, 1);
q = vfmaq_f32 (q, p, r2);
p = vmulq_laneq_f32 (r, c024, 2);
float32x4_t poly = vfmaq_f32 (p, q, r2);
if (__glibc_unlikely (v_any_u32 (cmp)))
return special_case (poly, n, e, cmp, scale, d);
return vfmaq_f32 (scale, poly, scale);
}
libmvec_hidden_def (V_NAME_F1 (exp2))
HALF_WIDTH_ALIAS_F1 (exp2)
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