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Annotation of 41BSD/cmd/lisp/subbig.c, revision 1.1.1.1

1.1       root        1: static char *sccsid = "@(#)subbig.c    34.1 10/3/80";
                      2: 
                      3: #include "global.h"
                      4: 
                      5: lispval
                      6: subbig(pos,neg)
                      7: lispval pos, neg;
                      8: {
                      9:        register lispval work;
                     10:        int *sp(); lispval adbig();
                     11:        register int *mysp = sp() - 2;
                     12:        register int *ersatz = mysp;
                     13:        snpand(3);
                     14: 
                     15:        for(work = neg; work!=0; work = work->s.CDR) {
                     16:                stack(-work->i, (mysp -= 2));
                     17:        }
                     18:        mysp[3] = 0;
                     19:        return(adbig(pos,ersatz));
                     20: }
                     21: /*
                     22:  * subbig -- subtract one bignum from another.
                     23:  *
                     24:  * What this does is it negates each coefficient of a copy of the bignum
                     25:  * which is just pushed on the stack for convenience.  This may give rise
                     26:  * to a bignum which is not in canonical form, but is nonetheless a repre
                     27:  * sentation of a bignum.  Addbig then adds it to a bignum, and produces
                     28:  * a result in canonical form.
                     29:  */

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