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div.c revision 1.1.1.3 
      1 /* mpq_div -- divide two rational numbers.
      2 
      3 Copyright 1991, 1994-1996, 2000, 2001, 2015 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.h"
     32 #include "gmp-impl.h"
     33 
     34 
     35 void
     36 mpq_div (mpq_ptr quot, mpq_srcptr op1, mpq_srcptr op2)
     37 {
     38   mpz_t gcd1, gcd2;
     39   mpz_t tmp1, tmp2;
     40   mp_size_t op1_size;
     41   mp_size_t op2_size;
     42   mp_size_t alloc;
     43   TMP_DECL;
     44 
     45   op2_size = SIZ(NUM(op2));
     46 
     47   if (UNLIKELY (op2_size == 0))
     48     DIVIDE_BY_ZERO;
     49 
     50   if (UNLIKELY (quot == op2))
     51     {
     52       if (op1 == op2)
     53 	{
     54 	  PTR(NUM(quot))[0] = 1;
     55 	  SIZ(NUM(quot)) = 1;
     56 	  PTR(DEN(quot))[0] = 1;
     57 	  SIZ(DEN(quot)) = 1;
     58 	  return;
     59 	}
     60 
     61       /* We checked for op1 == op2: we are not in the x=x/x case.
     62 	 We compute x=y/x by computing x=inv(x)*y */
     63       MPN_PTR_SWAP (PTR(NUM(quot)), ALLOC(NUM(quot)),
     64 		    PTR(DEN(quot)), ALLOC(DEN(quot)));
     65       if (op2_size > 0)
     66 	{
     67 	  SIZ(NUM(quot)) = SIZ(DEN(quot));
     68 	  SIZ(DEN(quot)) = op2_size;
     69 	}
     70       else
     71 	{
     72 	  SIZ(NUM(quot)) = - SIZ(DEN(quot));
     73 	  SIZ(DEN(quot)) = - op2_size;
     74 	}
     75       mpq_mul (quot, quot, op1);
     76       return;
     77     }
     78 
     79   op1_size = ABSIZ(NUM(op1));
     80 
     81   if (op1_size == 0)
     82     {
     83       /* We special case this to simplify allocation logic; gcd(0,x) = x
     84 	 is a singular case for the allocations.  */
     85       SIZ(NUM(quot)) = 0;
     86       PTR(DEN(quot))[0] = 1;
     87       SIZ(DEN(quot)) = 1;
     88       return;
     89     }
     90 
     91   op2_size = ABS(op2_size);
     92 
     93   TMP_MARK;
     94 
     95   alloc = MIN (op1_size, op2_size);
     96   MPZ_TMP_INIT (gcd1, alloc);
     97 
     98   alloc = MAX (op1_size, op2_size);
     99   MPZ_TMP_INIT (tmp1, alloc);
    100 
    101   op2_size = SIZ(DEN(op2));
    102   op1_size = SIZ(DEN(op1));
    103 
    104   alloc = MIN (op1_size, op2_size);
    105   MPZ_TMP_INIT (gcd2, alloc);
    106 
    107   alloc = MAX (op1_size, op2_size);
    108   MPZ_TMP_INIT (tmp2, alloc);
    109 
    110   /* QUOT might be identical to OP1, so don't store the result there
    111      until we are finished with the input operand.  We can overwrite
    112      the numerator of QUOT when we are finished with the numerator of
    113      OP1. */
    114 
    115   mpz_gcd (gcd1, NUM(op1), NUM(op2));
    116   mpz_gcd (gcd2, DEN(op2), DEN(op1));
    117 
    118   mpz_divexact_gcd (tmp1, NUM(op1), gcd1);
    119   mpz_divexact_gcd (tmp2, DEN(op2), gcd2);
    120 
    121   mpz_mul (NUM(quot), tmp1, tmp2);
    122 
    123   mpz_divexact_gcd (tmp1, NUM(op2), gcd1);
    124   mpz_divexact_gcd (tmp2, DEN(op1), gcd2);
    125 
    126   mpz_mul (DEN(quot), tmp1, tmp2);
    127 
    128   /* Keep the denominator positive.  */
    129   if (SIZ(DEN(quot)) < 0)
    130     {
    131       SIZ(DEN(quot)) = -SIZ(DEN(quot));
    132       SIZ(NUM(quot)) = -SIZ(NUM(quot));
    133     }
    134 
    135   TMP_FREE;
    136 }
    137