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65 lines
1.6 KiB
C
65 lines
1.6 KiB
C
/* Auxiliary routine for the Bessel functions (j0f, y0f, j1f, y1f).
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Copyright (C) 2021-2025 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#ifndef _MATH_REDUCE_AUX_H
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#define _MATH_REDUCE_AUX_H
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#include <math.h>
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#include <math_private.h>
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#include <s_sincosf.h>
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/* Return h and update n such that:
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Now x - pi/4 - alpha = h + n*pi/2 mod (2*pi). */
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static inline double
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reduce_aux (float x, int *n, double alpha)
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{
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double h;
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h = reduce_large (asuint (x), n);
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/* Now |x| = h+n*pi/2 mod 2*pi. */
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/* Recover sign. */
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if (x < 0)
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{
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h = -h;
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*n = -*n;
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}
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/* Subtract pi/4. */
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double piover2 = 0xc.90fdaa22168cp-3;
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if (h >= 0)
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h -= piover2 / 2;
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else
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{
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h += piover2 / 2;
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(*n) --;
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}
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/* Subtract alpha and reduce if needed mod pi/2. */
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h -= alpha;
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if (h > piover2)
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{
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h -= piover2;
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(*n) ++;
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}
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else if (h < -piover2)
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{
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h += piover2;
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(*n) --;
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}
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return h;
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}
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#endif
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