| 1 | /* Compute radix independent exponent. |
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| 2 | Copyright (C) 2011-2022 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 | #include <math.h> |
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| 20 | |
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| 21 | #include <math_private.h> |
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| 22 | #include <libm-alias-double.h> |
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| 23 | #include <fix-int-fp-convert-zero.h> |
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| 24 | |
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| 25 | double |
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| 26 | __logb (double x) |
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| 27 | { |
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| 28 | int64_t ix, ex; |
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| 29 | |
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| 30 | EXTRACT_WORDS64 (ix, x); |
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| 31 | ix &= UINT64_C(0x7fffffffffffffff); |
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| 32 | if (ix == 0) |
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| 33 | return -1.0 / fabs (x: x); |
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| 34 | ex = ix >> 52; |
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| 35 | if (ex == 0x7ff) |
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| 36 | return x * x; |
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| 37 | if (__glibc_unlikely (ex == 0)) |
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| 38 | { |
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| 39 | int m = __builtin_clzll (ix); |
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| 40 | ex -= m - 12; |
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| 41 | } |
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| 42 | if (FIX_INT_FP_CONVERT_ZERO && ex == 1023) |
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| 43 | return 0.0; |
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| 44 | return (double) (ex - 1023); |
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| 45 | } |
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| 46 | #ifndef __logb |
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| 47 | libm_alias_double (__logb, logb) |
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| 48 | #endif |
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| 49 | |
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