1  /* mpq_set_f -- set an mpq from an mpf.
       2  
       3  Copyright 2000-2002, 2018 Free Software Foundation, Inc.
       4  
       5  This file is part of the GNU MP Library.
       6  
       7  The GNU MP Library is free software; you can redistribute it and/or modify
       8  it under the terms of either:
       9  
      10    * the GNU Lesser General Public License as published by the Free
      11      Software Foundation; either version 3 of the License, or (at your
      12      option) any later version.
      13  
      14  or
      15  
      16    * the GNU General Public License as published by the Free Software
      17      Foundation; either version 2 of the License, or (at your option) any
      18      later version.
      19  
      20  or both in parallel, as here.
      21  
      22  The GNU MP Library is distributed in the hope that it will be useful, but
      23  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
      24  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
      25  for more details.
      26  
      27  You should have received copies of the GNU General Public License and the
      28  GNU Lesser General Public License along with the GNU MP Library.  If not,
      29  see https://www.gnu.org/licenses/.  */
      30  
      31  #include "gmp-impl.h"
      32  #include "longlong.h"
      33  
      34  
      35  void
      36  mpq_set_f (mpq_ptr q, mpf_srcptr f)
      37  {
      38    mp_size_t  fexp = EXP(f);
      39    mp_ptr     fptr = PTR(f);
      40    mp_size_t  fsize = SIZ(f);
      41    mp_size_t  abs_fsize = ABS(fsize);
      42    mp_limb_t  flow;
      43  
      44    if (fsize == 0)
      45      {
      46        /* set q=0 */
      47        SIZ(NUM(q)) = 0;
      48        SIZ(DEN(q)) = 1;
      49        MPZ_NEWALLOC (DEN(q), 1)[0] = 1;
      50        return;
      51      }
      52  
      53    /* strip low zero limbs from f */
      54    flow = *fptr;
      55    MPN_STRIP_LOW_ZEROS_NOT_ZERO (fptr, abs_fsize, flow);
      56  
      57    if (fexp >= abs_fsize)
      58      {
      59        /* radix point is to the right of the limbs, no denominator */
      60        mp_ptr  num_ptr;
      61  
      62        num_ptr = MPZ_NEWALLOC (mpq_numref (q), fexp);
      63        MPN_ZERO (num_ptr, fexp - abs_fsize);
      64        MPN_COPY (num_ptr + fexp - abs_fsize, fptr, abs_fsize);
      65  
      66        SIZ(NUM(q)) = fsize >= 0 ? fexp : -fexp;
      67        SIZ(DEN(q)) = 1;
      68        MPZ_NEWALLOC (DEN(q), 1)[0] = 1;
      69      }
      70    else
      71      {
      72        /* radix point is within or to the left of the limbs, use denominator */
      73        mp_ptr     num_ptr, den_ptr;
      74        mp_size_t  den_size;
      75  
      76        den_size = abs_fsize - fexp;
      77        num_ptr = MPZ_NEWALLOC (mpq_numref (q), abs_fsize);
      78        den_ptr = MPZ_NEWALLOC (mpq_denref (q), den_size+1);
      79  
      80        if (flow & 1)
      81          {
      82            /* no powers of two to strip from numerator */
      83  
      84            MPN_COPY (num_ptr, fptr, abs_fsize);
      85            MPN_ZERO (den_ptr, den_size);
      86            den_ptr[den_size] = 1;
      87          }
      88        else
      89          {
      90            /* right shift numerator, adjust denominator accordingly */
      91            int  shift;
      92  
      93            den_size--;
      94            count_trailing_zeros (shift, flow);
      95  
      96            mpn_rshift (num_ptr, fptr, abs_fsize, shift);
      97            abs_fsize -= (num_ptr[abs_fsize-1] == 0);
      98  
      99            MPN_ZERO (den_ptr, den_size);
     100            den_ptr[den_size] = GMP_LIMB_HIGHBIT >> (shift-1);
     101          }
     102  
     103        SIZ(NUM(q)) = fsize >= 0 ? abs_fsize : -abs_fsize;
     104        SIZ(DEN(q)) = den_size + 1;
     105      }
     106  }