gcc/gmp/mpq/set_f.c

/* mpq_set_f -- set an mpq from an mpf.

Copyright 2000, 2001, 2002 Free Software Foundation, Inc.

This file is part of the GNU MP Library.

The GNU MP Library is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 3 of the License, or (at your
option) any later version.

The GNU MP Library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
License for more details.

You should have received a copy of the GNU Lesser General Public License
along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */

#include "gmp.h"
#include "gmp-impl.h"
#include "longlong.h"


void
mpq_set_f (mpq_ptr q, mpf_srcptr f)
{
  mp_size_t  fexp = EXP(f);
  mp_ptr     fptr = PTR(f);
  mp_size_t  fsize = SIZ(f);
  mp_size_t  abs_fsize = ABS(fsize);
  mp_limb_t  flow;

  if (fsize == 0)
    {
      /* set q=0 */
      q->_mp_num._mp_size = 0;
      q->_mp_den._mp_size = 1;
      q->_mp_den._mp_d[0] = 1;
      return;
    }

  /* strip low zero limbs from f */
  flow = *fptr;
  MPN_STRIP_LOW_ZEROS_NOT_ZERO (fptr, abs_fsize, flow);

  if (fexp >= abs_fsize)
    {
      /* radix point is to the right of the limbs, no denominator */
      mp_ptr  num_ptr;

      MPZ_REALLOC (mpq_numref (q), fexp);
      num_ptr = q->_mp_num._mp_d;
      MPN_ZERO (num_ptr, fexp - abs_fsize);
      MPN_COPY (num_ptr + fexp - abs_fsize, fptr, abs_fsize);

      q->_mp_num._mp_size = fsize >= 0 ? fexp : -fexp;
      q->_mp_den._mp_size = 1;
      q->_mp_den._mp_d[0] = 1;
    }
  else
    {
      /* radix point is within or to the left of the limbs, use demominator */
      mp_ptr     num_ptr, den_ptr;
      mp_size_t  den_size;

      den_size = abs_fsize - fexp;
      MPZ_REALLOC (mpq_numref (q), abs_fsize);
      MPZ_REALLOC (mpq_denref (q), den_size+1);
      num_ptr = q->_mp_num._mp_d;
      den_ptr = q->_mp_den._mp_d;

      if (flow & 1)
        {
          /* no powers of two to strip from numerator */

          MPN_COPY (num_ptr, fptr, abs_fsize);
          MPN_ZERO (den_ptr, den_size);
          den_ptr[den_size] = 1;
        }
      else
        {
          /* right shift numerator, adjust denominator accordingly */
          int  shift;

          den_size--;
          count_trailing_zeros (shift, flow);

          mpn_rshift (num_ptr, fptr, abs_fsize, shift);
          abs_fsize -= (num_ptr[abs_fsize-1] == 0);

          MPN_ZERO (den_ptr, den_size);
          den_ptr[den_size] = GMP_LIMB_HIGHBIT >> (shift-1);
        }

      q->_mp_num._mp_size = fsize >= 0 ? abs_fsize : -abs_fsize;
      q->_mp_den._mp_size = den_size + 1;
    }
}