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/* Auxiliary routine for the Bessel functions (j0f, y0f, j1f, y1f).
Copyright (C) 2021-2023 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/>. */
#ifndef _MATH_REDUCE_AUX_H
#define _MATH_REDUCE_AUX_H
#include <math.h>
#include <math_private.h>
#include <s_sincosf.h>
/* Return h and update n such that:
Now x - pi/4 - alpha = h + n*pi/2 mod (2*pi). */
static inline double
reduce_aux (float x, int *n, double alpha)
{
double h;
h = reduce_large (asuint (x), n);
/* Now |x| = h+n*pi/2 mod 2*pi. */
/* Recover sign. */
if (x < 0)
{
h = -h;
*n = -*n;
}
/* Subtract pi/4. */
double piover2 = 0xc.90fdaa22168cp-3;
if (h >= 0)
h -= piover2 / 2;
else
{
h += piover2 / 2;
(*n) --;
}
/* Subtract alpha and reduce if needed mod pi/2. */
h -= alpha;
if (h > piover2)
{
h -= piover2;
(*n) ++;
}
else if (h < -piover2)
{
h += piover2;
(*n) --;
}
return h;
}
#endif
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