usr/src/cmd/lisp/franz/subbig.c

static char *sccsid = "@(#)subbig.c     35.1 5/6/81";

#include "global.h"

lispval
subbig(pos,neg)
lispval pos, neg;
{
        register lispval work;
        int *sp(); lispval adbig();
        register int *mysp = sp() - 2;
        register int *ersatz = mysp;
        snpand(3);

        for(work = neg; work!=0; work = work->s.CDR) {
                stack(-work->i, (mysp -= 2));
        }
        mysp[3] = 0;
        return(adbig(pos,ersatz));
}
/*
 * subbig -- subtract one bignum from another.
 *
 * What this does is it negates each coefficient of a copy of the bignum
 * which is just pushed on the stack for convenience.  This may give rise
 * to a bignum which is not in canonical form, but is nonetheless a repre
 * sentation of a bignum.  Addbig then adds it to a bignum, and produces
 * a result in canonical form.
 */