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79 lines
2.6 KiB
C
79 lines
2.6 KiB
C
/* Get exponent of a floating-point value. PowerPC version.
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Copyright (C) 2012-2025 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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/* ISA 2.07 provides fast GPR to FP instruction (mfvsr{d,wz}) which make
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generic implementation faster. */
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#if defined(_ARCH_PWR8) || !defined(_ARCH_PWR7)
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# include <./sysdeps/ieee754/ldbl-128ibm/s_logbl.c>
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#else
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# include <math.h>
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# include <math_private.h>
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# include <math_ldbl_opt.h>
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/* This implementation avoids FP to INT conversions by using VSX
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bitwise instructions over FP values. */
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long double
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__logbl (long double x)
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{
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double xh, xl;
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double ret;
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int64_t hx;
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if (__glibc_unlikely (x == 0.0))
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/* Raise FE_DIVBYZERO and return -HUGE_VAL[LF]. */
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return -1.0L / __builtin_fabsl (x);
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ldbl_unpack (x, &xh, &xl);
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EXTRACT_WORDS64 (hx, xh);
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/* Mask to extract the exponent. */
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asm ("xxland %x0,%x1,%x2\n"
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"fcfid %0,%0"
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: "=d" (ret)
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: "d" (xh), "d" (0x7ff0000000000000ULL));
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ret = (ret * 0x1p-52) - 1023.0;
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if (ret > 1023.0)
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/* Multiplication is used to set logb (+-INF) = INF. */
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return (xh * xh);
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else if (ret == -1023.0)
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{
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/* POSIX specifies that denormal number is treated as
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though it were normalized. */
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return (long double) (- (__builtin_clzll (hx & 0x7fffffffffffffffLL) \
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- 12) - 1023);
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}
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else if ((hx & 0x000fffffffffffffLL) == 0)
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{
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/* If the high part is a power of 2, and the low part is nonzero
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with the opposite sign, the low part affects the
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exponent. */
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int64_t lx, rhx;
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EXTRACT_WORDS64 (lx, xl);
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rhx = (hx & 0x7ff0000000000000LL) >> 52;
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if ((hx ^ lx) < 0 && (lx & 0x7fffffffffffffffLL) != 0)
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rhx--;
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return (long double) (rhx - 1023);
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}
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/* Test to avoid logb_downward (0.0) == -0.0. */
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return ret == -0.0 ? 0.0 : ret;
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}
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# ifndef __logbl
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long_double_symbol (libm, __logbl, logbl);
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# endif
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#endif
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