| 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/ldbl-128ibm/s_logbl.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 | |
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| 28 | /* This implementation avoids FP to INT conversions by using VSX |
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| 29 | bitwise instructions over FP values. */ |
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| 30 | long double |
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| 31 | __logbl (long double x) |
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| 32 | { |
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| 33 | double xh, xl; |
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| 34 | double ret; |
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| 35 | int64_t hx; |
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| 36 | |
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| 37 | if (__glibc_unlikely (x == 0.0)) |
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| 38 | /* Raise FE_DIVBYZERO and return -HUGE_VAL[LF]. */ |
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| 39 | return -1.0L / __builtin_fabsl (x); |
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| 40 | |
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| 41 | ldbl_unpack (x, &xh, &xl); |
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| 42 | EXTRACT_WORDS64 (hx, xh); |
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| 43 | |
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| 44 | /* Mask to extract the exponent. */ |
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| 45 | asm ("xxland %x0,%x1,%x2\n" |
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| 46 | "fcfid %0,%0" |
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| 47 | : "=d" (ret) |
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| 48 | : "d" (xh), "d" (0x7ff0000000000000ULL)); |
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| 49 | ret = (ret * 0x1p-52) - 1023.0; |
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| 50 | if (ret > 1023.0) |
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| 51 | /* Multiplication is used to set logb (+-INF) = INF. */ |
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| 52 | return (xh * xh); |
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| 53 | else if (ret == -1023.0) |
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| 54 | { |
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| 55 | /* POSIX specifies that denormal number is treated as |
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| 56 | though it were normalized. */ |
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| 57 | return (long double) (- (__builtin_clzll (hx & 0x7fffffffffffffffLL) \ |
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| 58 | - 12) - 1023); |
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| 59 | } |
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| 60 | else if ((hx & 0x000fffffffffffffLL) == 0) |
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| 61 | { |
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| 62 | /* If the high part is a power of 2, and the low part is nonzero |
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| 63 | with the opposite sign, the low part affects the |
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| 64 | exponent. */ |
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| 65 | int64_t lx, rhx; |
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| 66 | EXTRACT_WORDS64 (lx, xl); |
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| 67 | rhx = (hx & 0x7ff0000000000000LL) >> 52; |
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| 68 | if ((hx ^ lx) < 0 && (lx & 0x7fffffffffffffffLL) != 0) |
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| 69 | rhx--; |
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| 70 | return (long double) (rhx - 1023); |
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| 71 | } |
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| 72 | /* Test to avoid logb_downward (0.0) == -0.0. */ |
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| 73 | return ret == -0.0 ? 0.0 : ret; |
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| 74 | } |
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| 75 | # ifndef __logbl |
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| 76 | long_double_symbol (libm, __logbl, logbl); |
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| 77 | # endif |
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| 78 | #endif |
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| 79 | |
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