49 lines
1.4 KiB
C
49 lines
1.4 KiB
C
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/* Compute radix independent exponent.
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Copyright (C) 2011-2022 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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#include <math.h>
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#include <math_private.h>
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#include <libm-alias-double.h>
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#include <fix-int-fp-convert-zero.h>
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double
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__logb (double x)
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{
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int64_t ix, ex;
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EXTRACT_WORDS64 (ix, x);
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ix &= UINT64_C(0x7fffffffffffffff);
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if (ix == 0)
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return -1.0 / fabs (x);
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ex = ix >> 52;
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if (ex == 0x7ff)
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return x * x;
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if (__glibc_unlikely (ex == 0))
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{
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int m = __builtin_clzll (ix);
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ex -= m - 12;
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}
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if (FIX_INT_FP_CONVERT_ZERO && ex == 1023)
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return 0.0;
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return (double) (ex - 1023);
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}
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#ifndef __logb
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libm_alias_double (__logb, logb)
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#endif
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