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86 lines
2.8 KiB
C
86 lines
2.8 KiB
C
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/* mpq_sub -- subtract two rational numbers.
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Copyright (C) 1991, 1994, 1995, 1996 Free Software Foundation, Inc.
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This file is part of the GNU MP Library.
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The GNU MP Library is free software; you can redistribute it and/or modify
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it under the terms of the GNU Library General Public License as published by
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the Free Software Foundation; either version 2 of the License, or (at your
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option) any later version.
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The GNU MP Library is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public
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License for more details.
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You should have received a copy of the GNU Library General Public License
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along with the GNU MP Library; see the file COPYING.LIB. If not, write to
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the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
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MA 02111-1307, USA. */
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#include "gmp.h"
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#include "gmp-impl.h"
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void
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#if __STDC__
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mpq_sub (mpq_ptr rop, mpq_srcptr op1, mpq_srcptr op2)
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#else
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mpq_sub (rop, op1, op2)
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mpq_ptr rop;
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mpq_srcptr op1;
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mpq_srcptr op2;
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#endif
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{
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mpz_t gcd;
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mpz_t tmp1, tmp2;
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mp_size_t op1_num_size = ABS (op1->_mp_num._mp_size);
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mp_size_t op1_den_size = ABS (op1->_mp_den._mp_size);
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mp_size_t op2_num_size = ABS (op2->_mp_num._mp_size);
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mp_size_t op2_den_size = ABS (op2->_mp_den._mp_size);
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TMP_DECL (marker);
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TMP_MARK (marker);
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MPZ_TMP_INIT (gcd, MIN (op1_den_size, op2_den_size));
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MPZ_TMP_INIT (tmp1, op1_num_size + op2_den_size);
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MPZ_TMP_INIT (tmp2, op2_num_size + op1_den_size);
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/* ROP might be identical to either operand, so don't store the
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result there until we are finished with the input operands. We
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dare to overwrite the numerator of ROP when we are finished
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with the numerators of OP1 and OP2. */
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mpz_gcd (gcd, &(op1->_mp_den), &(op2->_mp_den));
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if (gcd->_mp_size > 1 || gcd->_mp_d[0] != 1)
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{
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mpz_t t;
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mpz_divexact (tmp1, &(op2->_mp_den), gcd);
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mpz_mul (tmp1, &(op1->_mp_num), tmp1);
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mpz_divexact (tmp2, &(op1->_mp_den), gcd);
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mpz_mul (tmp2, &(op2->_mp_num), tmp2);
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MPZ_TMP_INIT (t, MAX (ABS (tmp1->_mp_size), ABS (tmp2->_mp_size)) + 1);
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mpz_sub (t, tmp1, tmp2);
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mpz_divexact (tmp1, &(op1->_mp_den), gcd);
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mpz_gcd (gcd, t, gcd);
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mpz_divexact (&(rop->_mp_num), t, gcd);
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mpz_divexact (tmp2, &(op2->_mp_den), gcd);
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mpz_mul (&(rop->_mp_den), tmp1, tmp2);
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}
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else
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{
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/* The common divisor is 1. This is the case (for random input) with
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probability 6/(pi**2). */
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mpz_mul (tmp1, &(op1->_mp_num), &(op2->_mp_den));
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mpz_mul (tmp2, &(op2->_mp_num), &(op1->_mp_den));
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mpz_sub (&(rop->_mp_num), tmp1, tmp2);
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mpz_mul (&(rop->_mp_den), &(op1->_mp_den), &(op2->_mp_den));
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}
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TMP_FREE (marker);
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}
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