/* gcd.f -- translated by f2c (version 19980913).
   You must link the resulting object file with the libraries:
	-lf2c -lm   (in that order)
*/

#include "f2c.h"

/* $Procedure            GCD ( Greatest Common Divisor ) */
integer gcd_(integer *a, integer *b)
{
    /* System generated locals */
    integer ret_val;

    /* Local variables */
    integer absa, absb, p, q, remndr;

/* $ Abstract */

/*      Return the greatest common divisor of two integers. */

/* $ Disclaimer */

/*     THIS SOFTWARE AND ANY RELATED MATERIALS WERE CREATED BY THE */
/*     CALIFORNIA INSTITUTE OF TECHNOLOGY (CALTECH) UNDER A U.S. */
/*     GOVERNMENT CONTRACT WITH THE NATIONAL AERONAUTICS AND SPACE */
/*     ADMINISTRATION (NASA). THE SOFTWARE IS TECHNOLOGY AND SOFTWARE */
/*     PUBLICLY AVAILABLE UNDER U.S. EXPORT LAWS AND IS PROVIDED "AS-IS" */
/*     TO THE RECIPIENT WITHOUT WARRANTY OF ANY KIND, INCLUDING ANY */
/*     WARRANTIES OF PERFORMANCE OR MERCHANTABILITY OR FITNESS FOR A */
/*     PARTICULAR USE OR PURPOSE (AS SET FORTH IN UNITED STATES UCC */
/*     SECTIONS 2312-2313) OR FOR ANY PURPOSE WHATSOEVER, FOR THE */
/*     SOFTWARE AND RELATED MATERIALS, HOWEVER USED. */

/*     IN NO EVENT SHALL CALTECH, ITS JET PROPULSION LABORATORY, OR NASA */
/*     BE LIABLE FOR ANY DAMAGES AND/OR COSTS, INCLUDING, BUT NOT */
/*     LIMITED TO, INCIDENTAL OR CONSEQUENTIAL DAMAGES OF ANY KIND, */
/*     INCLUDING ECONOMIC DAMAGE OR INJURY TO PROPERTY AND LOST PROFITS, */
/*     REGARDLESS OF WHETHER CALTECH, JPL, OR NASA BE ADVISED, HAVE */
/*     REASON TO KNOW, OR, IN FACT, SHALL KNOW OF THE POSSIBILITY. */

/*     RECIPIENT BEARS ALL RISK RELATING TO QUALITY AND PERFORMANCE OF */
/*     THE SOFTWARE AND ANY RELATED MATERIALS, AND AGREES TO INDEMNIFY */
/*     CALTECH AND NASA FOR ALL THIRD-PARTY CLAIMS RESULTING FROM THE */
/*     ACTIONS OF RECIPIENT IN THE USE OF THE SOFTWARE. */

/* $ Required_Reading */

/*     None. */

/* $ Keywords */

/*      MATH,  NUMBERS */

/* $ Declarations */
/* $ Brief_I/O */

/*      VARIABLE  I/O  DESCRIPTION */
/*      --------  ---  -------------------------------------------------- */
/*      A          I   Any integer */
/*      B          I   Any integer */
/*      GCD        I   The greatest common divisor of A and B. */

/* $ Detailed_Input */

/*      A          An integer */

/*      B          An integer */

/* $ Detailed_Output */

/*      GCD        The greatest common divisor of A and B. */

/* $ Parameters */

/*      None. */

/* $ Exceptions */

/*     Error free. */

/*     1) If both A and B are zero, we return 0 as the GCD. */

/*     2) If exactly one of A and B is zero, then the GCD is by */
/*        definition the maximum of the absolute values of A and B. */

/* $ Particulars */

/*      This routine uses Euclid's Algorithm to find the greatest common */
/*      divisor (GCD) of the integers A and B.  In other words the */
/*      largest integer, G, such that A = k*G for some k and B = j*G for */
/*      some G.  Note if either A or B is zero, then we return the */
/*      maximum of the two integers ABS(A) and ABS(B).  If one is */
/*      non-zero we have just what the definition says.  If both are zero */
/*      the definition above does not give us a GCD, so we take the GCD */
/*      of 0 and 0 to be 0. */


/* $ Examples */

/*      A      B            GCD */
/*    -----  -----         ----- */
/*      8      4             4 */
/*     120    44             4 */
/*     15    135            15 */
/*    101     97             1 */
/*    119    221            17 */
/*    144     81             9 */
/*      0    111           111 */
/*      0      0             0 */

/* $ Restrictions */

/*      None. */

/* $ Files */

/*      None. */

/* $ Author_and_Institution */

/*      W.L. Taber      (JPL) */

/* $ Literature_References */

/*      The Art of Computer Programming Vol 1. "Fundamental Algorithms" */
/*      by Donald Knuth */

/* $ Version */

/* -    SPICELIB Version 1.0.1, 10-MAR-1992 (WLT) */

/*        Comment section for permuted index source lines was added */
/*        following the header. */

/* -    SPICELIB Version 1.0.0, 31-JAN-1990 (WLT) */

/* -& */
/* $ Index_Entries */

/*     greatest common divisor */

/* -& */
/* $ Revisions */

/* -     Beta Version 1.0.1, 29-DEC-1988 (WLT) */

/*      This revision simply cleared up questions regarding the input of */
/*      zeros to the routine. */

/* -& */

/*     Local variables */

    absa = abs(*a);
    absb = abs(*b);
    if (absa > absb) {
	p = absa;
	q = absb;
    } else {
	p = absb;
	q = absa;
    }
    remndr = 1;
    if (q != 0) {
	while(remndr != 0) {
	    ret_val = q;
	    remndr = p - p / q * q;
	    p = q;
	    q = remndr;
	}
    } else {
	ret_val = p;
    }
    return ret_val;
} /* gcd_ */

