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/* Single-precision vector (SVE) log function.
Copyright (C) 2023 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;
} 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
};
#define Min (0x00800000)
#define Max (0x7f800000)
#define Thresh (0x7f000000) /* Max - Min. */
#define Mask (0x007fffff)
#define Off (0x3f2aaaab) /* 0.666667. */
static svfloat32_t NOINLINE
special_case (svfloat32_t x, svfloat32_t y, svbool_t cmp)
{
return sv_call_f32 (logf, x, 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 = svreinterpret_u32_f32 (x);
svbool_t cmp = svcmpge_n_u32 (pg, svsub_n_u32_x (pg, u, Min), Thresh);
/* x = 2^n * (1+r), where 2/3 < 1+r < 4/3. */
u = svsub_n_u32_x (pg, u, Off);
svfloat32_t n
= svcvt_f32_s32_x (pg, svasr_n_s32_x (pg, svreinterpret_s32_u32 (u),
23)); /* Sign-extend. */
u = svand_n_u32_x (pg, u, Mask);
u = svadd_n_u32_x (pg, u, Off);
svfloat32_t r = svsub_n_f32_x (pg, svreinterpret_f32_u32 (u), 1.0f);
/* y = log(1+r) + n*ln2. */
svfloat32_t r2 = svmul_f32_x (pg, r, r);
/* n*ln2 + r + r2*(P6 + r*P5 + r2*(P4 + r*P3 + r2*(P2 + r*P1 + r2*P0))). */
svfloat32_t p_0135 = svld1rq_f32 (svptrue_b32 (), &d->poly_0135[0]);
svfloat32_t p = svmla_lane_f32 (sv_f32 (d->poly_246[0]), r, p_0135, 1);
svfloat32_t q = svmla_lane_f32 (sv_f32 (d->poly_246[1]), r, p_0135, 2);
svfloat32_t y = svmla_lane_f32 (sv_f32 (d->poly_246[2]), r, p_0135, 3);
p = svmla_lane_f32 (p, r2, p_0135, 0);
q = svmla_f32_x (pg, q, r2, p);
y = svmla_f32_x (pg, y, r2, q);
p = svmla_n_f32_x (pg, r, n, d->ln2);
y = svmla_f32_x (pg, p, r2, y);
if (__glibc_unlikely (svptest_any (pg, cmp)))
return special_case (x, y, cmp);
return y;
}
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