.ref-BSD-4_3_Net_2/usr/src/usr.bin/lisp/franz/68k/mulbig.c

/*
 * $Header: mulbig.c,v 1.2 83/11/26 12:13:29 sklower Exp $
 * $Locker:  $
 *
 * Copyright (c) 1982, Regents, University of California
 *
 */

#include "global.h"

struct s_dot    { long I; struct s_dot *CDR; };
struct vl       { long high; long low; };

struct s_dot *mulbig(a,b)
struct s_dot *a, *b;
{
        int la = 1, lb = 1;
        long *sa, *sb, *sc, *base, *alloca();
        struct s_dot *export();
        register struct s_dot *p;
        register int *q, *r, *s;
        long carry = 0, test;
        struct vl work;
        Keepxs();

        /* compute lengths */

        for(p = a; p->CDR; p = p->CDR) la++;
        for(p = b; p->CDR; p = p->CDR) lb++;

        /* allocate storage areas on the stack */

        base = alloca((la + la + lb + lb + 1)*sizeof(long));
        sc = base + la + lb + 1;
        sb = sc + lb;
        sa = sb + la;
        q  = sa;

        /* copy s_dots onto stack */
        p = a;
        do { *--q = p->I; p = p->CDR; } while (p);
        p = b;
        do { *--q = p->I; p = p->CDR; } while (p);
        while(q > base) *--q = 0;  /* initialize target */

        /* perform the multiplication */
        for(q = sb; q > sc; *--s = carry)
            for((r = sa, s = (q--) - lb, carry = 0); r > sb;)
            {
                    carry += *--s;
                    emul(*q,*--r,carry,&work);
                    test = work.low;
                    carry = work.high << 2;
                    if(test < 0) carry += 2;
                    if(test & 0x40000000) carry +=1;
                    *s = test & 0x3fffffff;
            }

        p = export(sc,base);
        Freexs();
        return(p);
}