| 1 | /* Compute full X * Y for long double type. |
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| 2 | Copyright (C) 2013-2024 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 _MUL_SPLITL_H |
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| 20 | #define _MUL_SPLITL_H |
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| 21 | |
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| 22 | #include <float.h> |
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| 23 | |
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| 24 | /* Calculate X * Y exactly and store the result in *HI + *LO. It is |
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| 25 | given that the values are small enough that no overflow occurs and |
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| 26 | large enough (or zero) that no underflow occurs. */ |
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| 27 | |
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| 28 | static inline void |
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| 29 | mul_splitl (long double *hi, long double *lo, long double x, long double y) |
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| 30 | { |
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| 31 | #ifdef __FP_FAST_FMAL |
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| 32 | /* Fast built-in fused multiply-add. */ |
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| 33 | *hi = x * y; |
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| 34 | *lo = __builtin_fmal (x, y, -*hi); |
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| 35 | #else |
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| 36 | /* Apply Dekker's algorithm. */ |
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| 37 | *hi = x * y; |
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| 38 | # define C ((1LL << (LDBL_MANT_DIG + 1) / 2) + 1) |
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| 39 | long double x1 = x * C; |
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| 40 | long double y1 = y * C; |
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| 41 | # undef C |
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| 42 | x1 = (x - x1) + x1; |
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| 43 | y1 = (y - y1) + y1; |
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| 44 | long double x2 = x - x1; |
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| 45 | long double y2 = y - y1; |
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| 46 | *lo = (((x1 * y1 - *hi) + x1 * y2) + x2 * y1) + x2 * y2; |
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| 47 | #endif |
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| 48 | } |
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| 49 | |
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| 50 | #endif /* _MUL_SPLITL_H */ |
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| 51 | |
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