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79 lines
1.9 KiB
C
79 lines
1.9 KiB
C
/* Multiply a 'float' by a power of 2.
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Copyright 2002-2003, 2007-2026 Free Software Foundation, Inc.
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This file is free software: you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as
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published by the Free Software Foundation; either version 2.1 of the
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License, or (at your option) any later version.
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This file 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
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GNU Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>. */
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/* Written by Paolo Bonzini and Bruno Haible. */
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#include <config.h>
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/* Specification. */
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#include <math.h>
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# include <float.h>
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#ifdef USE_LONG_DOUBLE
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# include "fpucw.h"
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#endif
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/* Avoid some warnings from "gcc -Wshadow".
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This file doesn't use the exp() function. */
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#undef exp
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#define exp exponent
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#ifdef USE_LONG_DOUBLE
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# define FUNC ldexpl
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# define DOUBLE long double
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# define ISNAN isnanl
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# define DECL_ROUNDING DECL_LONG_DOUBLE_ROUNDING
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# define BEGIN_ROUNDING() BEGIN_LONG_DOUBLE_ROUNDING ()
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# define END_ROUNDING() END_LONG_DOUBLE_ROUNDING ()
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# define L_(literal) literal##L
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#else
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# define FUNC ldexp
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# define DOUBLE double
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# define ISNAN isnand
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# define DECL_ROUNDING
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# define BEGIN_ROUNDING()
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# define END_ROUNDING()
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# define L_(literal) literal
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#endif
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DOUBLE
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FUNC (DOUBLE x, int exp)
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{
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DECL_ROUNDING
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BEGIN_ROUNDING ();
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/* Check for zero, nan and infinity. */
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if (!(ISNAN (x) || x + x == x))
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{
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DOUBLE factor = exp < 0 ? L_(0.5) : L_(2.0);
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while (true)
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{
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if (exp % 2 != 0)
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x *= factor;
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exp /= 2;
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if (exp == 0)
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break;
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factor = factor * factor;
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}
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}
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END_ROUNDING ();
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return x;
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}
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