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49 lines
1.5 KiB
C
49 lines
1.5 KiB
C
/* Copyright (C) 1992, 1995 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 Library General Public License as
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published by the Free Software Foundation; either version 2 of the
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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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Library General Public License for more details.
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You should have received a copy of the GNU Library General Public
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License along with the GNU C Library; see the file COPYING.LIB. If
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not, write to the Free Software Foundation, Inc., 675 Mass Ave,
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Cambridge, MA 02139, USA. */
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#include <ansidecl.h>
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#include <math.h>
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#include <float.h>
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#include "ieee754.h"
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/* Return the base 2 signed integral exponent of X. */
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double
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DEFUN(__logb, (x), double x)
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{
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union ieee754_double u;
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if (__isnan (x))
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return x;
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else if (__isinf (x))
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return HUGE_VAL;
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else if (x == 0.0)
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return - HUGE_VAL;
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u.d = x;
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if (u.ieee.exponent == 0)
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/* A denormalized number.
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Multiplying by 2 ** DBL_MANT_DIG normalizes it;
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we then subtract the DBL_MANT_DIG we added to the exponent. */
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return (__logb (x * ldexp (1.0, DBL_MANT_DIG)) - DBL_MANT_DIG);
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return (int) u.ieee.exponent - (DBL_MAX_EXP - 1);
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}
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weak_alias (__logb, logb)
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