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div.c revision 1.1.1.4 
      1 /* mpq_div -- divide two rational numbers.
      2 
      3 Copyright 1991, 1994-1996, 2000, 2001, 2015, 2018 Free Software
      4 Foundation, Inc.
      5 
      6 This file is part of the GNU MP Library.
      7 
      8 The GNU MP Library is free software; you can redistribute it and/or modify
      9 it under the terms of either:
     10 
     11   * the GNU Lesser General Public License as published by the Free
     12     Software Foundation; either version 3 of the License, or (at your
     13     option) any later version.
     14 
     15 or
     16 
     17   * the GNU General Public License as published by the Free Software
     18     Foundation; either version 2 of the License, or (at your option) any
     19     later version.
     20 
     21 or both in parallel, as here.
     22 
     23 The GNU MP Library is distributed in the hope that it will be useful, but
     24 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
     25 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
     26 for more details.
     27 
     28 You should have received copies of the GNU General Public License and the
     29 GNU Lesser General Public License along with the GNU MP Library.  If not,
     30 see https://www.gnu.org/licenses/.  */
     31 
     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 (UNLIKELY (op1 == op2))
     53 	{
     54 	  mpq_set_ui (quot, 1, 1);
     55 	  return;
     56 	}
     57 
     58       /* We checked for op1 == op2: we are not in the x=x/x case.
     59 	 We compute x=y/x by computing x=inv(x)*y */
     60       MPN_PTR_SWAP (PTR(NUM(quot)), ALLOC(NUM(quot)),
     61 		    PTR(DEN(quot)), ALLOC(DEN(quot)));
     62       if (op2_size > 0)
     63 	{
     64 	  SIZ(NUM(quot)) = SIZ(DEN(quot));
     65 	  SIZ(DEN(quot)) = op2_size;
     66 	}
     67       else
     68 	{
     69 	  SIZ(NUM(quot)) = - SIZ(DEN(quot));
     70 	  SIZ(DEN(quot)) = - op2_size;
     71 	}
     72       mpq_mul (quot, quot, op1);
     73       return;
     74     }
     75 
     76   op1_size = ABSIZ(NUM(op1));
     77 
     78   if (op1_size == 0)
     79     {
     80       /* We special case this to simplify allocation logic; gcd(0,x) = x
     81 	 is a singular case for the allocations.  */
     82       SIZ(NUM(quot)) = 0;
     83       MPZ_NEWALLOC (DEN(quot), 1)[0] = 1;
     84       SIZ(DEN(quot)) = 1;
     85       return;
     86     }
     87 
     88   op2_size = ABS(op2_size);
     89 
     90   TMP_MARK;
     91 
     92   alloc = MIN (op1_size, op2_size);
     93   MPZ_TMP_INIT (gcd1, alloc);
     94 
     95   alloc = MAX (op1_size, op2_size);
     96   MPZ_TMP_INIT (tmp1, alloc);
     97 
     98   op2_size = SIZ(DEN(op2));
     99   op1_size = SIZ(DEN(op1));
    100 
    101   alloc = MIN (op1_size, op2_size);
    102   MPZ_TMP_INIT (gcd2, alloc);
    103 
    104   alloc = MAX (op1_size, op2_size);
    105   MPZ_TMP_INIT (tmp2, alloc);
    106 
    107   /* QUOT might be identical to OP1, so don't store the result there
    108      until we are finished with the input operand.  We can overwrite
    109      the numerator of QUOT when we are finished with the numerator of
    110      OP1. */
    111 
    112   mpz_gcd (gcd1, NUM(op1), NUM(op2));
    113   mpz_gcd (gcd2, DEN(op2), DEN(op1));
    114 
    115   mpz_divexact_gcd (tmp1, NUM(op1), gcd1);
    116   mpz_divexact_gcd (tmp2, DEN(op2), gcd2);
    117 
    118   mpz_mul (NUM(quot), tmp1, tmp2);
    119 
    120   mpz_divexact_gcd (tmp1, NUM(op2), gcd1);
    121   mpz_divexact_gcd (tmp2, DEN(op1), gcd2);
    122 
    123   mpz_mul (DEN(quot), tmp1, tmp2);
    124 
    125   /* Keep the denominator positive.  */
    126   if (SIZ(DEN(quot)) < 0)
    127     {
    128       SIZ(DEN(quot)) = -SIZ(DEN(quot));
    129       SIZ(NUM(quot)) = -SIZ(NUM(quot));
    130     }
    131 
    132   TMP_FREE;
    133 }
    134