mirror of
https://sourceware.org/git/glibc.git
synced 2024-11-22 13:00:06 +00:00
a15b1394b5
Reduce MOVPRFXs by using unpredicated (non-destructive) instructions where possible. Similar to the recent change to AdvSIMD F32 logs, adjust special-case arguments and bounds to allow for more optimal register usage. For all 3 routines one MOVPRFX remains in the reduction, which cannot be avoided as immediate AND and ASR are both destructive. Reviewed-by: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
102 lines
3.9 KiB
C
102 lines
3.9 KiB
C
/* Single-precision vector (SVE) log10 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_0246[4];
|
|
float poly_1357[4];
|
|
float ln2, inv_ln10;
|
|
uint32_t off, lower;
|
|
} data = {
|
|
.poly_1357 = {
|
|
/* Coefficients copied from the AdvSIMD routine, then rearranged so that coeffs
|
|
1, 3, 5 and 7 can be loaded as a single quad-word, hence used with _lane
|
|
variant of MLA intrinsic. */
|
|
0x1.2879c8p-3f, 0x1.6408f8p-4f, 0x1.f0e514p-5f, 0x1.f5f76ap-5f
|
|
},
|
|
.poly_0246 = { -0x1.bcb79cp-3f, -0x1.bcd472p-4f, -0x1.246f8p-4f,
|
|
-0x1.0fc92cp-4f },
|
|
.ln2 = 0x1.62e43p-1f,
|
|
.inv_ln10 = 0x1.bcb7b2p-2f,
|
|
.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 Thres 0x7f000000 /* asuint32(inf) - 0x00800000. */
|
|
#define MantissaMask 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 (
|
|
log10f, svreinterpret_f32 (svadd_x (svptrue_b32 (), u_off, data.off)),
|
|
svmla_x (svptrue_b32 (), p, r2, y), cmp);
|
|
}
|
|
|
|
/* Optimised implementation of SVE log10f using the same algorithm and
|
|
polynomial as AdvSIMD log10f.
|
|
Maximum error is 3.31ulps:
|
|
SV_NAME_F1 (log10)(0x1.555c16p+0) got 0x1.ffe2fap-4
|
|
want 0x1.ffe2f4p-4. */
|
|
svfloat32_t SV_NAME_F1 (log10) (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 special = svcmpge (pg, svsub_x (pg, u_off, d->lower), Thres);
|
|
|
|
/* 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)); /* signextend. */
|
|
svuint32_t ix = svand_x (pg, u_off, MantissaMask);
|
|
ix = svadd_x (pg, ix, d->off);
|
|
svfloat32_t r = svsub_x (pg, svreinterpret_f32 (ix), 1.0f);
|
|
|
|
/* y = log10(1+r) + n*log10(2)
|
|
log10(1+r) ~ r * InvLn(10) + P(r)
|
|
where P(r) is a polynomial. Use order 9 for log10(1+x), i.e. order 8 for
|
|
log10(1+x)/x, with x in [-1/3, 1/3] (offset=2/3). */
|
|
svfloat32_t r2 = svmul_x (svptrue_b32 (), r, r);
|
|
svfloat32_t r4 = svmul_x (svptrue_b32 (), r2, r2);
|
|
svfloat32_t p_1357 = svld1rq (svptrue_b32 (), &d->poly_1357[0]);
|
|
svfloat32_t q_01 = svmla_lane (sv_f32 (d->poly_0246[0]), r, p_1357, 0);
|
|
svfloat32_t q_23 = svmla_lane (sv_f32 (d->poly_0246[1]), r, p_1357, 1);
|
|
svfloat32_t q_45 = svmla_lane (sv_f32 (d->poly_0246[2]), r, p_1357, 2);
|
|
svfloat32_t q_67 = svmla_lane (sv_f32 (d->poly_0246[3]), r, p_1357, 3);
|
|
svfloat32_t q_47 = svmla_x (pg, q_45, r2, q_67);
|
|
svfloat32_t q_03 = svmla_x (pg, q_01, r2, q_23);
|
|
svfloat32_t y = svmla_x (pg, q_03, r4, q_47);
|
|
|
|
/* Using hi = Log10(2)*n + r*InvLn(10) is faster but less accurate. */
|
|
svfloat32_t hi = svmla_x (pg, r, n, d->ln2);
|
|
hi = svmul_x (pg, hi, d->inv_ln10);
|
|
|
|
if (__glibc_unlikely (svptest_any (pg, special)))
|
|
return special_case (u_off, hi, r2, y, special);
|
|
return svmla_x (svptrue_b32 (), hi, r2, y);
|
|
}
|