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/* gcd.c (greatest common divisor) */
/***********************************************************************
* This code is part of GLPK (GNU Linear Programming Kit).
* Copyright (C) 2000 Free Software Foundation, Inc.
* Written by Andrew Makhorin <mao@gnu.org>.
*
* GLPK is free software: you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* GLPK is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
* License for more details.
*
* You should have received a copy of the GNU General Public License
* along with GLPK. If not, see <http://www.gnu.org/licenses/>.
***********************************************************************/
#include "env.h"
#include "misc.h"
/***********************************************************************
* NAME
*
* gcd - find greatest common divisor of two integers
*
* SYNOPSIS
*
* #include "misc.h"
* int gcd(int x, int y);
*
* RETURNS
*
* The routine gcd returns gcd(x, y), the greatest common divisor of
* the two positive integers given.
*
* ALGORITHM
*
* The routine gcd is based on Euclid's algorithm.
*
* REFERENCES
*
* Don Knuth, The Art of Computer Programming, Vol.2: Seminumerical
* Algorithms, 3rd Edition, Addison-Wesley, 1997. Section 4.5.2: The
* Greatest Common Divisor, pp. 333-56. */
int gcd(int x, int y)
{ int r;
xassert(x > 0 && y > 0);
while (y > 0)
r = x % y, x = y, y = r;
return x;
}
/***********************************************************************
* NAME
*
* gcdn - find greatest common divisor of n integers
*
* SYNOPSIS
*
* #include "misc.h"
* int gcdn(int n, int x[]);
*
* RETURNS
*
* The routine gcdn returns gcd(x[1], x[2], ..., x[n]), the greatest
* common divisor of n positive integers given, n > 0.
*
* BACKGROUND
*
* The routine gcdn is based on the following identity:
*
* gcd(x, y, z) = gcd(gcd(x, y), z).
*
* REFERENCES
*
* Don Knuth, The Art of Computer Programming, Vol.2: Seminumerical
* Algorithms, 3rd Edition, Addison-Wesley, 1997. Section 4.5.2: The
* Greatest Common Divisor, pp. 333-56. */
int gcdn(int n, int x[])
{ int d, j;
xassert(n > 0);
for (j = 1; j <= n; j++)
{ xassert(x[j] > 0);
if (j == 1)
d = x[1];
else
d = gcd(d, x[j]);
if (d == 1)
break;
}
return d;
}
/* eof */
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