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/* Single-precision vector (Advanced SIMD) log 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 c2, c4, c6, ln2;
uint32x4_t off, offset_lower_bound, mantissa_mask;
uint16x8_t special_bound;
float c1, c3, c5, c0;
} data = {
/* 3.34 ulp error. */
.c0 = -0x1.3e737cp-3f,
.c1 = 0x1.5a9aa2p-3f,
.c2 = V4 (-0x1.4f9934p-3f),
.c3 = 0x1.961348p-3f,
.c4 = V4 (-0x1.00187cp-2f),
.c5 = 0x1.555d7cp-2f,
.c6 = V4 (-0x1.ffffc8p-2f),
.ln2 = V4 (0x1.62e43p-1f),
/* Lower bound is the smallest positive normal float 0x00800000. For
optimised register use subnormals are detected after offset has been
subtracted, so lower bound is 0x0080000 - offset (which wraps around). */
.offset_lower_bound = V4 (0x00800000 - 0x3f2aaaab),
.special_bound = V8 (0x7f00), /* top16(asuint32(inf) - 0x00800000). */
.off = V4 (0x3f2aaaab), /* 0.666667. */
.mantissa_mask = V4 (0x007fffff)
};
static float32x4_t VPCS_ATTR NOINLINE
special_case (float32x4_t p, uint32x4_t u_off, float32x4_t y, float32x4_t r2,
uint16x4_t cmp, const struct data *d)
{
/* Fall back to scalar code. */
return v_call_f32 (logf, vreinterpretq_f32_u32 (vaddq_u32 (u_off, d->off)),
vfmaq_f32 (p, y, r2), vmovl_u16 (cmp));
}
float32x4_t VPCS_ATTR NOINLINE V_NAME_F1 (log) (float32x4_t x)
{
const struct data *d = ptr_barrier (&data);
float32x4_t c1350 = vld1q_f32 (&d->c1);
/* To avoid having to mov x out of the way, keep u after offset has been
applied, and recover x by adding the offset back in the special-case
handler. */
uint32x4_t u_off = vsubq_u32 (vreinterpretq_u32_f32 (x), d->off);
/* x = 2^n * (1+r), where 2/3 < 1+r < 4/3. */
float32x4_t n = vcvtq_f32_s32 (
vshrq_n_s32 (vreinterpretq_s32_u32 (u_off), 23)); /* signextend. */
uint16x4_t cmp = vcge_u16 (vsubhn_u32 (u_off, d->offset_lower_bound),
vget_low_u16 (d->special_bound));
uint32x4_t u = vaddq_u32 (vandq_u32 (u_off, d->mantissa_mask), d->off);
float32x4_t r = vsubq_f32 (vreinterpretq_f32_u32 (u), v_f32 (1.0f));
/* y = log(1+r) + n*ln2. */
float32x4_t r2 = vmulq_f32 (r, r);
/* n*ln2 + r + r2*(P1 + r*P2 + r2*(P3 + r*P4 + r2*(P5 + r*P6 + r2*P7))). */
float32x4_t p = vfmaq_laneq_f32 (d->c2, r, c1350, 0);
float32x4_t q = vfmaq_laneq_f32 (d->c4, r, c1350, 1);
float32x4_t y = vfmaq_laneq_f32 (d->c6, r, c1350, 2);
p = vfmaq_laneq_f32 (p, r2, c1350, 3);
q = vfmaq_f32 (q, p, r2);
y = vfmaq_f32 (y, q, r2);
p = vfmaq_f32 (r, d->ln2, n);
if (__glibc_unlikely (v_any_u16h (cmp)))
return special_case (p, u_off, y, r2, cmp, d);
return vfmaq_f32 (p, y, r2);
}
libmvec_hidden_def (V_NAME_F1 (log))
HALF_WIDTH_ALIAS_F1 (log)
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