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glibc  2.9
mpn2dbl.c
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00001 /* Copyright (C) 1995,1996,1997,2002,2003 Free Software Foundation, Inc.
00002    This file is part of the GNU C Library.
00003 
00004    The GNU C Library is free software; you can redistribute it and/or
00005    modify it under the terms of the GNU Lesser General Public
00006    License as published by the Free Software Foundation; either
00007    version 2.1 of the License, or (at your option) any later version.
00008 
00009    The GNU C Library is distributed in the hope that it will be useful,
00010    but WITHOUT ANY WARRANTY; without even the implied warranty of
00011    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00012    Lesser General Public License for more details.
00013 
00014    You should have received a copy of the GNU Lesser General Public
00015    License along with the GNU C Library; if not, write to the Free
00016    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
00017    02111-1307 USA.  */
00018 
00019 #include "gmp.h"
00020 #include "gmp-impl.h"
00021 #include <ieee754.h>
00022 #include <float.h>
00023 
00024 /* Convert a multi-precision integer of the needed number of bits (53 for
00025    double) and an integral power of two to a `double' in IEEE754 double-
00026    precision format.  */
00027 
00028 double
00029 __mpn_construct_double (mp_srcptr frac_ptr, int expt, int negative)
00030 {
00031   union ieee754_double u;
00032 
00033   u.ieee.negative = negative;
00034   u.ieee.exponent = expt + IEEE754_DOUBLE_BIAS;
00035 #if BITS_PER_MP_LIMB == 32
00036   u.ieee.mantissa1 = frac_ptr[0];
00037   u.ieee.mantissa0 = frac_ptr[1] & (((mp_limb_t) 1
00038                                  << (DBL_MANT_DIG - 32)) - 1);
00039 #elif BITS_PER_MP_LIMB == 64
00040   u.ieee.mantissa1 = frac_ptr[0] & (((mp_limb_t) 1 << 32) - 1);
00041   u.ieee.mantissa0 = (frac_ptr[0] >> 32) & (((mp_limb_t) 1
00042                                         << (DBL_MANT_DIG - 32)) - 1);
00043 #else
00044   #error "mp_limb size " BITS_PER_MP_LIMB "not accounted for"
00045 #endif
00046 
00047   return u.d;
00048 }