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c064f6a613
1. Fix the results for negative subnormals by ignoring the signal when
normalizing the value.
2. Fix the output when the high part is a power of 2 and the low part
is a nonzero number with opposite sign. This fix is based on commit
380bd0fd24.
After applying this patch, logbl() tests pass cleanly on POWER >= 7.
Tested on powerpc, powerpc64 and powerpc64le
[BZ #21280]
* sysdeps/powerpc/power7/fpu/s_logbl.c (__logbl): Ignore the
signal of subnormals and adjust the exponent of power of 2 down
when low part has opposite sign.
84 lines
2.7 KiB
C
84 lines
2.7 KiB
C
/* logbl(). PowerPC/POWER7 version.
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Copyright (C) 2012-2017 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.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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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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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 (__builtin_expect (x == 0.0L, 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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/* 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" (xh), "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 (xh * xh);
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else if (__builtin_expect (ret == two10m1, 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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