sysdeps/ieee754/mpn2dbl.c

   1 /* Copyright (C) 1995 Free Software Foundation, Inc.
   2 This file is part of the GNU C Library.
   3
   4 The GNU C Library is free software; you can redistribute it and/or
   5 modify it under the terms of the GNU Library General Public License as
   6 published by the Free Software Foundation; either version 2 of the
   7 License, or (at your option) any later version.
   8
   9 The GNU C Library is distributed in the hope that it will be useful,
  10 but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12 Library General Public License for more details.
  13
  14 You should have received a copy of the GNU Library General Public
  15 License along with the GNU C Library; see the file COPYING.LIB.  If
  16 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  17 Cambridge, MA 02139, USA.  */
  18
  19 #include "gmp.h"
  20 #include "gmp-impl.h"
  21 #include "ieee754.h"
  22 #include <float.h>
  23
  24 /* Convert a multi-precision integer of the needed number of bits (53 for
  25    double) and an integral power of two to a `double' in IEEE754 double-
  26    precision format.  */
  27
  28 double
  29 __mpn_construct_double (mp_srcptr frac_ptr, int expt, int negative)
  30 {
  31   union ieee754_double u;
  32
  33   u.ieee.negative = negative;
  34   u.ieee.exponent = expt + IEEE754_DOUBLE_BIAS;
  35 #if BITS_PER_MP_LIMB == 32
  36   u.ieee.mantissa1 = frac_ptr[0];
  37   u.ieee.mantissa0 = frac_ptr[1] & ((1 << (DBL_MANT_DIG - 32)) - 1);
  38 #elif BITS_PER_MP_LIMB == 64
  39   u.ieee.mantissa1 = frac_ptr[0] & ((1 << 32) - 1);
  40   u.ieee.mantissa0 = (frac_ptr[0] >> 32) & ((1 << (DBL_MANT_DIG - 32)) - 1);
  41 #else
  42   #error "mp_limb size " BITS_PER_MP_LIMB "not accounted for"
  43 #endif
  44
  45   return u.d;
  46 }