| 1 | /* Get exponent of a floating-point value. PowerPC version. |
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| 2 | Copyright (C) 2012-2024 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 | /* ISA 2.07 provides fast GPR to FP instruction (mfvsr{d,wz}) which make |
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| 20 | generic implementation faster. */ |
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| 21 | #if defined(_ARCH_PWR8) || !defined(_ARCH_PWR7) |
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| 22 | # include <sysdeps/ieee754/dbl-64/s_logb.c> |
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| 23 | #else |
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| 24 | # include <math.h> |
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| 25 | # include <math_private.h> |
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| 26 | # include <math_ldbl_opt.h> |
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| 27 | # include <libm-alias-double.h> |
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| 28 | |
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| 29 | /* This implementation avoids FP to INT conversions by using VSX |
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| 30 | bitwise instructions over FP values. */ |
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| 31 | double |
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| 32 | __logb (double x) |
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| 33 | { |
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| 34 | double ret; |
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| 35 | |
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| 36 | if (__glibc_unlikely (x == 0.0)) |
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| 37 | /* Raise FE_DIVBYZERO and return -HUGE_VAL[LF]. */ |
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| 38 | return -1.0 / fabs (x); |
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| 39 | |
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| 40 | /* Mask to extract the exponent. */ |
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| 41 | asm ("xxland %x0,%x1,%x2\n" |
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| 42 | "fcfid %0,%0" |
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| 43 | : "=d" (ret) |
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| 44 | : "d" (x), "d" (0x7ff0000000000000ULL)); |
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| 45 | ret = (ret * 0x1p-52) - 1023.0; |
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| 46 | if (ret > 1023.0) |
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| 47 | /* Multiplication is used to set logb (+-INF) = INF. */ |
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| 48 | return (x * x); |
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| 49 | else if (ret == -1023.0) |
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| 50 | { |
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| 51 | /* POSIX specifies that denormal numbers are treated as |
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| 52 | though they were normalized. */ |
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| 53 | int64_t ix; |
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| 54 | EXTRACT_WORDS64 (ix, x); |
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| 55 | ix &= UINT64_C (0x7fffffffffffffff); |
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| 56 | return (double) (-1023 - (__builtin_clzll (ix) - 12)); |
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| 57 | } |
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| 58 | /* Test to avoid logb_downward (0.0) == -0.0. */ |
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| 59 | return ret == -0.0 ? 0.0 : ret; |
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| 60 | } |
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| 61 | # ifndef __logb |
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| 62 | libm_alias_double (__logb, logb) |
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| 63 | # endif |
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| 64 | #endif |
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| 65 | |
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