| 1 | /* Auxiliary routine for the Bessel functions (j0f, y0f, j1f, y1f). |
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| 2 | Copyright (C) 2021-2024 Free Software Foundation, Inc. |
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| 3 | This file is part of the GNU C Library. |
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| 4 | |
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| 5 | The GNU C Library is free software; you can redistribute it and/or |
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| 6 | modify it under the terms of the GNU Lesser General Public |
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| 7 | License as published by the Free Software Foundation; either |
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| 8 | version 2.1 of the License, or (at your option) any later version. |
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| 9 | |
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| 10 | The GNU C Library is distributed in the hope that it will be useful, |
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| 11 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
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| 12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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| 13 | Lesser General Public License for more details. |
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| 14 | |
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| 15 | You should have received a copy of the GNU Lesser General Public |
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| 16 | License along with the GNU C Library; if not, see |
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| 17 | <https://www.gnu.org/licenses/>. */ |
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| 18 | |
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| 19 | #ifndef _MATH_REDUCE_AUX_H |
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| 20 | #define _MATH_REDUCE_AUX_H |
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| 21 | |
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| 22 | #include <math.h> |
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| 23 | #include <math_private.h> |
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| 24 | #include <s_sincosf.h> |
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| 25 | |
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| 26 | /* Return h and update n such that: |
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| 27 | Now x - pi/4 - alpha = h + n*pi/2 mod (2*pi). */ |
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| 28 | static inline double |
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| 29 | reduce_aux (float x, int *n, double alpha) |
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| 30 | { |
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| 31 | double h; |
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| 32 | h = reduce_large (xi: asuint (f: x), np: n); |
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| 33 | /* Now |x| = h+n*pi/2 mod 2*pi. */ |
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| 34 | /* Recover sign. */ |
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| 35 | if (x < 0) |
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| 36 | { |
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| 37 | h = -h; |
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| 38 | *n = -*n; |
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| 39 | } |
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| 40 | /* Subtract pi/4. */ |
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| 41 | double piover2 = 0xc.90fdaa22168cp-3; |
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| 42 | if (h >= 0) |
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| 43 | h -= piover2 / 2; |
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| 44 | else |
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| 45 | { |
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| 46 | h += piover2 / 2; |
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| 47 | (*n) --; |
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| 48 | } |
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| 49 | /* Subtract alpha and reduce if needed mod pi/2. */ |
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| 50 | h -= alpha; |
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| 51 | if (h > piover2) |
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| 52 | { |
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| 53 | h -= piover2; |
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| 54 | (*n) ++; |
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| 55 | } |
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| 56 | else if (h < -piover2) |
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| 57 | { |
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| 58 | h += piover2; |
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| 59 | (*n) --; |
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| 60 | } |
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| 61 | return h; |
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| 62 | } |
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| 63 | |
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| 64 | #endif |
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| 65 | |
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