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/* Double-precision (SVE) cospi function
Copyright (C) 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"
#include "poly_sve_f64.h"
static const struct data
{
double poly[10];
double range_val;
} data = {
/* Polynomial coefficients generated using Remez algorithm,
see sinpi.sollya for details. */
.poly = { 0x1.921fb54442d184p1, -0x1.4abbce625be53p2, 0x1.466bc6775ab16p1,
-0x1.32d2cce62dc33p-1, 0x1.507834891188ep-4, -0x1.e30750a28c88ep-8,
0x1.e8f48308acda4p-12, -0x1.6fc0032b3c29fp-16,
0x1.af86ae521260bp-21, -0x1.012a9870eeb7dp-25 },
.range_val = 0x1p53,
};
/* A fast SVE implementation of cospi.
Maximum error 3.20 ULP:
_ZGVsMxv_cospi(0x1.f18ba32c63159p-6) got 0x1.fdabf595f9763p-1
want 0x1.fdabf595f9766p-1. */
svfloat64_t SV_NAME_D1 (cospi) (svfloat64_t x, const svbool_t pg)
{
const struct data *d = ptr_barrier (&data);
/* Using cospi(x) = sinpi(0.5 - x)
range reduction and offset into sinpi range -1/2 .. 1/2
r = 0.5 - |x - rint(x)|. */
svfloat64_t n = svrinta_x (pg, x);
svfloat64_t r = svsub_x (pg, x, n);
r = svsub_x (pg, sv_f64 (0.5), svabs_x (pg, r));
/* Result should be negated based on if n is odd or not.
If ax >= 2^53, the result will always be positive. */
svbool_t cmp = svaclt (pg, x, d->range_val);
svuint64_t intn = svreinterpret_u64 (svcvt_s64_z (pg, n));
svuint64_t sign = svlsl_z (cmp, intn, 63);
/* y = sin(r). */
svfloat64_t r2 = svmul_x (pg, r, r);
svfloat64_t r4 = svmul_x (pg, r2, r2);
svfloat64_t y = sv_pw_horner_9_f64_x (pg, r2, r4, d->poly);
y = svmul_x (pg, y, r);
return svreinterpret_f64 (sveor_x (pg, svreinterpret_u64 (y), sign));
}
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