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/* Single-precision vector (Advanced SIMD) log 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"
static const struct data
{
uint32x4_t min_norm;
uint16x8_t special_bound;
float32x4_t poly[7];
float32x4_t ln2, tiny_bound;
uint32x4_t off, mantissa_mask;
} data = {
/* 3.34 ulp error. */
.poly = { V4 (-0x1.3e737cp-3f), V4 (0x1.5a9aa2p-3f), V4 (-0x1.4f9934p-3f),
V4 (0x1.961348p-3f), V4 (-0x1.00187cp-2f), V4 (0x1.555d7cp-2f),
V4 (-0x1.ffffc8p-2f) },
.ln2 = V4 (0x1.62e43p-1f),
.tiny_bound = V4 (0x1p-126),
.min_norm = V4 (0x00800000),
.special_bound = V8 (0x7f00), /* asuint32(inf) - min_norm. */
.off = V4 (0x3f2aaaab), /* 0.666667. */
.mantissa_mask = V4 (0x007fffff)
};
#define P(i) d->poly[7 - i]
static float32x4_t VPCS_ATTR NOINLINE
special_case (float32x4_t x, float32x4_t y, float32x4_t r2, float32x4_t p,
uint16x4_t cmp)
{
/* Fall back to scalar code. */
return v_call_f32 (logf, x, 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 n, p, q, r, r2, y;
uint32x4_t u;
uint16x4_t cmp;
u = vreinterpretq_u32_f32 (x);
cmp = 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);
n = vcvtq_f32_s32 (
vshrq_n_s32 (vreinterpretq_s32_u32 (u), 23)); /* signextend. */
u = vandq_u32 (u, d->mantissa_mask);
u = vaddq_u32 (u, d->off);
r = vsubq_f32 (vreinterpretq_f32_u32 (u), v_f32 (1.0f));
/* y = log(1+r) + n*ln2. */
r2 = vmulq_f32 (r, r);
/* n*ln2 + r + r2*(P1 + r*P2 + r2*(P3 + r*P4 + r2*(P5 + r*P6 + r2*P7))). */
p = vfmaq_f32 (P (5), P (6), r);
q = vfmaq_f32 (P (3), P (4), r);
y = vfmaq_f32 (P (1), P (2), r);
p = vfmaq_f32 (p, P (7), r2);
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 (x, y, r2, p, cmp);
return vfmaq_f32 (p, y, r2);
}
libmvec_hidden_def (V_NAME_F1 (log))
HALF_WIDTH_ALIAS_F1 (log)
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