efee5258bc
The MPFR library is a C library for multiple-precision floating-point computations with exact rounding (also called correct rounding). It is based on the GMP multiple-precision library and should replace the MPF class in further releases of GMP. GCC >= 4.2 requires MPFR.
92 lines
2.3 KiB
C
92 lines
2.3 KiB
C
/* mpfr_scale2 -- multiply a double float by 2^exp
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Copyright 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Free Software Foundation, Inc.
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Contributed by the Arenaire and Cacao projects, INRIA.
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This file is part of the GNU MPFR Library.
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The GNU MPFR Library 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 published by
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the Free Software Foundation; either version 3 of the License, or (at your
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option) any later version.
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The GNU MPFR Library is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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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 the GNU MPFR Library; see the file COPYING.LESSER. If not, see
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http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
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51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
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#include <float.h> /* for DBL_EPSILON */
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#include "mpfr-impl.h"
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/* Note: we could use the ldexp function, but since we want not to depend on
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math.h, we write our own implementation. */
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/* multiplies 1/2 <= d <= 1 by 2^exp */
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double
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mpfr_scale2 (double d, int exp)
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{
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#if _GMP_IEEE_FLOATS
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{
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union ieee_double_extract x;
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if (MPFR_UNLIKELY (d == 1.0))
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{
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d = 0.5;
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exp ++;
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}
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/* now 1/2 <= d < 1 */
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/* infinities and zeroes have already been checked */
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MPFR_ASSERTD (-1073 <= exp && exp <= 1025);
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x.d = d;
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if (MPFR_UNLIKELY (exp < -1021)) /* subnormal case */
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{
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x.s.exp += exp + 52;
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x.d *= DBL_EPSILON;
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}
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else /* normalized case */
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{
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x.s.exp += exp;
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}
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return x.d;
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}
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#else /* _GMP_IEEE_FLOATS */
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{
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double factor;
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/* An overflow may occurs (example: 0.5*2^1024) */
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if (d < 1.0)
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{
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d += d;
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exp--;
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}
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/* Now 1.0 <= d < 2.0 */
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if (exp < 0)
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{
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factor = 0.5;
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exp = -exp;
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}
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else
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{
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factor = 2.0;
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}
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while (exp != 0)
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{
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if ((exp & 1) != 0)
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d *= factor;
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exp >>= 1;
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factor *= factor;
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}
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return d;
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}
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#endif
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}
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