1  /* Copyright (C) 1995-2023 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     <https://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  }