2012-05-15 23:32:28 +08:00
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/* logbf(). PowerPC/POWER7 version.
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2019-01-01 08:11:28 +08:00
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Copyright (C) 2012-2019 Free Software Foundation, Inc.
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2012-05-15 23:32:28 +08:00
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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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2017-12-05 08:26:26 +08:00
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#include <libm-alias-float.h>
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2012-05-15 23:32:28 +08:00
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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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static const double two7m1 = -127.0; /* -2**7 + 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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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 (__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_fabsf (x);
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/* ret = x & 0x7f800000; */
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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, since ret is double. */
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ret = (ret * two1div52) + two10m1;
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if (__builtin_expect (ret > -two7m1, 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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2017-12-05 08:26:26 +08:00
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libm_alias_float (__logb, logb)
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