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Annotation of OpenXM_contrib/gmp/mpq/sub.c, Revision 1.1.1.1

1.1       maekawa     1: /* mpq_sub -- subtract two rational numbers.
                      2:
                      3: Copyright (C) 1991, 1994, 1995, 1996 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 the GNU Library General Public License as published by
                      9: the Free Software Foundation; either version 2 of the License, or (at your
                     10: option) any later version.
                     11:
                     12: The GNU MP Library is distributed in the hope that it will be useful, but
                     13: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
                     14: or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
                     15: License for more details.
                     16:
                     17: You should have received a copy of the GNU Library General Public License
                     18: along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
                     19: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
                     20: MA 02111-1307, USA. */
                     21:
                     22: #include "gmp.h"
                     23: #include "gmp-impl.h"
                     24:
                     25: void
                     26: #if __STDC__
                     27: mpq_sub (mpq_ptr rop, mpq_srcptr op1, mpq_srcptr op2)
                     28: #else
                     29: mpq_sub (rop, op1, op2)
                     30:      mpq_ptr rop;
                     31:      mpq_srcptr op1;
                     32:      mpq_srcptr op2;
                     33: #endif
                     34: {
                     35:   mpz_t gcd;
                     36:   mpz_t tmp1, tmp2;
                     37:   mp_size_t op1_num_size = ABS (op1->_mp_num._mp_size);
                     38:   mp_size_t op1_den_size = ABS (op1->_mp_den._mp_size);
                     39:   mp_size_t op2_num_size = ABS (op2->_mp_num._mp_size);
                     40:   mp_size_t op2_den_size = ABS (op2->_mp_den._mp_size);
                     41:   TMP_DECL (marker);
                     42:
                     43:   TMP_MARK (marker);
                     44:   MPZ_TMP_INIT (gcd, MIN (op1_den_size, op2_den_size));
                     45:   MPZ_TMP_INIT (tmp1, op1_num_size + op2_den_size);
                     46:   MPZ_TMP_INIT (tmp2, op2_num_size + op1_den_size);
                     47:
                     48:   /* ROP might be identical to either operand, so don't store the
                     49:      result there until we are finished with the input operands.  We
                     50:      dare to overwrite the numerator of ROP when we are finished
                     51:      with the numerators of OP1 and OP2.  */
                     52:
                     53:   mpz_gcd (gcd, &(op1->_mp_den), &(op2->_mp_den));
                     54:   if (gcd->_mp_size > 1 || gcd->_mp_d[0] != 1)
                     55:     {
                     56:       mpz_t t;
                     57:
                     58:       mpz_divexact (tmp1, &(op2->_mp_den), gcd);
                     59:       mpz_mul (tmp1, &(op1->_mp_num), tmp1);
                     60:
                     61:       mpz_divexact (tmp2, &(op1->_mp_den), gcd);
                     62:       mpz_mul (tmp2, &(op2->_mp_num), tmp2);
                     63:
                     64:       MPZ_TMP_INIT (t, MAX (ABS (tmp1->_mp_size), ABS (tmp2->_mp_size)) + 1);
                     65:
                     66:       mpz_sub (t, tmp1, tmp2);
                     67:       mpz_divexact (tmp1, &(op1->_mp_den), gcd);
                     68:       mpz_gcd (gcd, t, gcd);
                     69:
                     70:       mpz_divexact (&(rop->_mp_num), t, gcd);
                     71:
                     72:       mpz_divexact (tmp2, &(op2->_mp_den), gcd);
                     73:       mpz_mul (&(rop->_mp_den), tmp1, tmp2);
                     74:     }
                     75:   else
                     76:     {
                     77:       /* The common divisor is 1.  This is the case (for random input) with
                     78:         probability 6/(pi**2).  */
                     79:       mpz_mul (tmp1, &(op1->_mp_num), &(op2->_mp_den));
                     80:       mpz_mul (tmp2, &(op2->_mp_num), &(op1->_mp_den));
                     81:       mpz_sub (&(rop->_mp_num), tmp1, tmp2);
                     82:       mpz_mul (&(rop->_mp_den), &(op1->_mp_den), &(op2->_mp_den));
                     83:     }
                     84:   TMP_FREE (marker);
                     85: }