mirror of
https://sourceware.org/git/glibc.git
synced 2024-11-22 21:10:07 +00:00
80 lines
2.9 KiB
C
80 lines
2.9 KiB
C
/* Single-precision vector (AdvSIMD) exp2 function
|
|
|
|
Copyright (C) 2023-2024 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/>. */
|
|
|
|
#include "v_math.h"
|
|
#include "poly_advsimd_f32.h"
|
|
|
|
static const struct data
|
|
{
|
|
uint32x4_t min_norm;
|
|
uint16x8_t special_bound;
|
|
uint32x4_t off, mantissa_mask;
|
|
float32x4_t poly[9];
|
|
} data = {
|
|
/* Coefficients generated using Remez algorithm approximate
|
|
log2(1+r)/r for r in [ -1/3, 1/3 ].
|
|
rel error: 0x1.c4c4b0cp-26. */
|
|
.poly = { V4 (0x1.715476p0f), /* (float)(1 / ln(2)). */
|
|
V4 (-0x1.715458p-1f), V4 (0x1.ec701cp-2f), V4 (-0x1.7171a4p-2f),
|
|
V4 (0x1.27a0b8p-2f), V4 (-0x1.e5143ep-3f), V4 (0x1.9d8ecap-3f),
|
|
V4 (-0x1.c675bp-3f), V4 (0x1.9e495p-3f) },
|
|
.min_norm = V4 (0x00800000),
|
|
.special_bound = V8 (0x7f00), /* asuint32(inf) - min_norm. */
|
|
.off = V4 (0x3f2aaaab), /* 0.666667. */
|
|
.mantissa_mask = V4 (0x007fffff),
|
|
};
|
|
|
|
static float32x4_t VPCS_ATTR NOINLINE
|
|
special_case (float32x4_t x, float32x4_t n, float32x4_t p, float32x4_t r,
|
|
uint16x4_t cmp)
|
|
{
|
|
/* Fall back to scalar code. */
|
|
return v_call_f32 (log2f, x, vfmaq_f32 (n, p, r), vmovl_u16 (cmp));
|
|
}
|
|
|
|
/* Fast implementation for single precision AdvSIMD log2,
|
|
relies on same argument reduction as AdvSIMD logf.
|
|
Maximum error: 2.48 ULPs
|
|
_ZGVnN4v_log2f(0x1.558174p+0) got 0x1.a9be84p-2
|
|
want 0x1.a9be8p-2. */
|
|
float32x4_t VPCS_ATTR NOINLINE V_NAME_F1 (log2) (float32x4_t x)
|
|
{
|
|
const struct data *d = ptr_barrier (&data);
|
|
uint32x4_t u = vreinterpretq_u32_f32 (x);
|
|
uint16x4_t special = vcge_u16 (vsubhn_u32 (u, d->min_norm),
|
|
vget_low_u16 (d->special_bound));
|
|
|
|
/* x = 2^n * (1+r), where 2/3 < 1+r < 4/3. */
|
|
u = vsubq_u32 (u, d->off);
|
|
float32x4_t n = vcvtq_f32_s32 (
|
|
vshrq_n_s32 (vreinterpretq_s32_u32 (u), 23)); /* signextend. */
|
|
u = vaddq_u32 (vandq_u32 (u, d->mantissa_mask), d->off);
|
|
float32x4_t r = vsubq_f32 (vreinterpretq_f32_u32 (u), v_f32 (1.0f));
|
|
|
|
/* y = log2(1+r) + n. */
|
|
float32x4_t r2 = vmulq_f32 (r, r);
|
|
float32x4_t p = v_pw_horner_8_f32 (r, r2, d->poly);
|
|
|
|
if (__glibc_unlikely (v_any_u16h (special)))
|
|
return special_case (x, n, p, r, special);
|
|
return vfmaq_f32 (n, p, r);
|
|
}
|
|
libmvec_hidden_def (V_NAME_F1 (log2))
|
|
HALF_WIDTH_ALIAS_F1 (log2)
|