57 lines
2.0 KiB
C
57 lines
2.0 KiB
C
/* Get exponent of a floating-point value. PowerPC version.
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Copyright (C) 2012-2022 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/flt-32/s_logbf.c>
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#else
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# include <math.h>
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# include <libm-alias-float.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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float
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__logbf (float x)
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{
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/* VSX operation are all done internally as double. */
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double ret;
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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 -1.0 / fabs (x);
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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" (x), "d" (0x7ff0000000000000ULL));
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/* ret = (ret >> 52) - 1023.0, since ret is double. */
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ret = (ret * 0x1p-52) - 1023.0;
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if (ret > 127.0)
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/* Multiplication is used to set logb (+-INF) = INF. */
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return (x * x);
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/* Since operations are done with double we don't need
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additional tests for subnormal numbers.
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The test is 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 __logbf
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libm_alias_float (__logb, logb)
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# endif
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#endif
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