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/* Single-precision vector (SVE) 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 "sv_math.h"
static const struct data
{
float poly_0135[4];
float poly_246[3];
float ln2;
uint32_t off, lower;
} data = {
.poly_0135 = {
/* Coefficients copied from the AdvSIMD routine in math/, then rearranged so
that coeffs 0, 1, 3 and 5 can be loaded as a single quad-word, hence used
with _lane variant of MLA intrinsic. */
-0x1.3e737cp-3f, 0x1.5a9aa2p-3f, 0x1.961348p-3f, 0x1.555d7cp-2f
},
.poly_246 = { -0x1.4f9934p-3f, -0x1.00187cp-2f, -0x1.ffffc8p-2f },
.ln2 = 0x1.62e43p-1f,
.off = 0x3f2aaaab,
/* 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). */
.lower = 0x00800000 - 0x3f2aaaab
};
#define Thresh (0x7f000000) /* asuint32(inf) - 0x00800000. */
#define Mask (0x007fffff)
static svfloat32_t NOINLINE
special_case (svuint32_t u_off, svfloat32_t p, svfloat32_t r2, svfloat32_t y,
svbool_t cmp)
{
return sv_call_f32 (
logf, svreinterpret_f32 (svadd_x (svptrue_b32 (), u_off, data.off)),
svmla_x (svptrue_b32 (), p, r2, y), cmp);
}
/* Optimised implementation of SVE logf, using the same algorithm and
polynomial as the AdvSIMD routine. Maximum error is 3.34 ULPs:
SV_NAME_F1 (log)(0x1.557298p+0) got 0x1.26edecp-2
want 0x1.26ede6p-2. */
svfloat32_t SV_NAME_F1 (log) (svfloat32_t x, const svbool_t pg)
{
const struct data *d = ptr_barrier (&data);
svuint32_t u_off = svreinterpret_u32 (x);
u_off = svsub_x (pg, u_off, d->off);
svbool_t cmp = svcmpge (pg, svsub_x (pg, u_off, d->lower), Thresh);
/* x = 2^n * (1+r), where 2/3 < 1+r < 4/3. */
svfloat32_t n = svcvt_f32_x (
pg, svasr_x (pg, svreinterpret_s32 (u_off), 23)); /* Sign-extend. */
svuint32_t u = svand_x (pg, u_off, Mask);
u = svadd_x (pg, u, d->off);
svfloat32_t r = svsub_x (pg, svreinterpret_f32 (u), 1.0f);
/* y = log(1+r) + n*ln2. */
svfloat32_t r2 = svmul_x (svptrue_b32 (), r, r);
/* n*ln2 + r + r2*(P6 + r*P5 + r2*(P4 + r*P3 + r2*(P2 + r*P1 + r2*P0))). */
svfloat32_t p_0135 = svld1rq (svptrue_b32 (), &d->poly_0135[0]);
svfloat32_t p = svmla_lane (sv_f32 (d->poly_246[0]), r, p_0135, 1);
svfloat32_t q = svmla_lane (sv_f32 (d->poly_246[1]), r, p_0135, 2);
svfloat32_t y = svmla_lane (sv_f32 (d->poly_246[2]), r, p_0135, 3);
p = svmla_lane (p, r2, p_0135, 0);
q = svmla_x (pg, q, r2, p);
y = svmla_x (pg, y, r2, q);
p = svmla_x (pg, r, n, d->ln2);
if (__glibc_unlikely (svptest_any (pg, cmp)))
return special_case (u_off, p, r2, y, cmp);
return svmla_x (pg, p, r2, y);
}
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