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79 lines
2.3 KiB
C
79 lines
2.3 KiB
C
/* logb(). PowerPC/POWER7 version.
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Copyright (C) 2012-2014 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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<http://www.gnu.org/licenses/>. */
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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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static const double two1div52 = 2.220446049250313e-16; /* 1/2**52 */
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static const double two10m1 = -1023.0; /* 2**10 -1 */
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/* FP mask to extract the exponent. */
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static const union {
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unsigned long long mask;
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double d;
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} mask = { 0x7ff0000000000000ULL };
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double
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__logb (double x)
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{
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double ret;
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if (__builtin_expect (x == 0.0, 0))
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/* Raise FE_DIVBYZERO and return -HUGE_VAL[LF]. */
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return -1.0 / __builtin_fabs (x);
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/* ret = x & 0x7ff0000000000000; */
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asm (
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"xxland %x0,%x1,%x2\n"
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"fcfid %0,%0"
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: "=f" (ret)
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: "f" (x), "f" (mask.d));
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/* ret = (ret >> 52) - 1023.0; */
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ret = (ret * two1div52) + two10m1;
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if (__builtin_expect (ret > -two10m1, 0))
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/* Multiplication is used to set logb (+-INF) = INF. */
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return (x * x);
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else if (__builtin_expect (ret == two10m1, 0))
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{
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/* POSIX specifies that denormal numbers are treated as
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though they were normalized. */
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int32_t lx, ix;
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int ma;
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EXTRACT_WORDS (ix, lx, x);
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if (ix == 0)
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ma = __builtin_clz (lx) + 32;
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else
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ma = __builtin_clz (ix);
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return (double) (-1023 - (ma - 12));
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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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weak_alias (__logb, logb)
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#ifdef NO_LONG_DOUBLE
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strong_alias (__logb, __logbl)
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weak_alias (__logb, logbl)
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#endif
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#if LONG_DOUBLE_COMPAT (libm, GLIBC_2_0)
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compat_symbol (libm, logb, logbl, GLIBC_2_0);
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#endif
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