1/* Auxiliary routine for the Bessel functions (j0f, y0f, j1f, y1f).
2 Copyright (C) 2021-2022 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19#ifndef _MATH_REDUCE_AUX_H
20#define _MATH_REDUCE_AUX_H
21
22#include <math.h>
23#include <math_private.h>
24#include <s_sincosf.h>
25
26/* Return h and update n such that:
27 Now x - pi/4 - alpha = h + n*pi/2 mod (2*pi). */
28static inline double
29reduce_aux (float x, int *n, double alpha)
30{
31 double h;
32 h = reduce_large (asuint (x), n);
33 /* Now |x| = h+n*pi/2 mod 2*pi. */
34 /* Recover sign. */
35 if (x < 0)
36 {
37 h = -h;
38 *n = -*n;
39 }
40 /* Subtract pi/4. */
41 double piover2 = 0xc.90fdaa22168cp-3;
42 if (h >= 0)
43 h -= piover2 / 2;
44 else
45 {
46 h += piover2 / 2;
47 (*n) --;
48 }
49 /* Subtract alpha and reduce if needed mod pi/2. */
50 h -= alpha;
51 if (h > piover2)
52 {
53 h -= piover2;
54 (*n) ++;
55 }
56 else if (h < -piover2)
57 {
58 h += piover2;
59 (*n) --;
60 }
61 return h;
62}
63
64#endif
65