sysdeps/ieee754/dbl-64/mpn2dbl.c

   1 /* Copyright (C) 1995-2016 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 Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the 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    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <http://www.gnu.org/licenses/>.  */
  17
  18 #include "gmp.h"
  19 #include "gmp-impl.h"
  20 #include <ieee754.h>
  21 #include <float.h>
  22
  23 /* Convert a multi-precision integer of the needed number of bits (53 for
  24    double) and an integral power of two to a `double' in IEEE754 double-
  25    precision format.  */
  26
  27 double
  28 __mpn_construct_double (mp_srcptr frac_ptr, int expt, int negative)
  29 {
  30   union ieee754_double u;
  31
  32   u.ieee.negative = negative;
  33   u.ieee.exponent = expt + IEEE754_DOUBLE_BIAS;
  34 #if BITS_PER_MP_LIMB == 32
  35   u.ieee.mantissa1 = frac_ptr[0];
  36   u.ieee.mantissa0 = frac_ptr[1] & (((mp_limb_t) 1
  37                                      << (DBL_MANT_DIG - 32)) - 1);
  38 #elif BITS_PER_MP_LIMB == 64
  39   u.ieee.mantissa1 = frac_ptr[0] & (((mp_limb_t) 1 << 32) - 1);
  40   u.ieee.mantissa0 = (frac_ptr[0] >> 32) & (((mp_limb_t) 1
  41                                              << (DBL_MANT_DIG - 32)) - 1);
  42 #else
  43   # error "mp_limb size " BITS_PER_MP_LIMB "not accounted for"
  44 #endif
  45
  46   return u.d;
  47 }