/* Double-precision (SVE) cospi function

   Copyright (C) 2024-2026 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));
}
