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Annotation of 42BSD/ucb/lisp/franz/68k/mulbig.c, revision 1.1.1.1

1.1       root        1: /* Copyright (c) 1982, Regents, University of California */
                      2: 
                      3: struct sdot    { long I; struct sdot *CDR; };
                      4: struct vl      { long high; long low; };
                      5: 
                      6: struct sdot *mulbig(a,b)
                      7: struct sdot *a, *b;
                      8: {
                      9:        int la = 1, lb = 1;
                     10:        long *sa, *sb, *sc, *base, *alloca();
                     11:        struct sdot *export();
                     12:        register struct sdot *p;
                     13:        register int *q, *r, *s;
                     14:        long carry = 0, test;
                     15:        struct vl work;
                     16: 
                     17:        /* compute lengths */
                     18:        
                     19:        for(p = a; p->CDR; p = p->CDR) la++;
                     20:        for(p = b; p->CDR; p = p->CDR) lb++;
                     21: 
                     22:        /* allocate storage areas on the stack */
                     23: 
                     24:        base = alloca((la + la + lb + lb + 1)*sizeof(long));
                     25:        sc = base + la + lb + 1;
                     26:        sb = sc + lb;
                     27:        sa = sb + la;
                     28:        q  = sa;
                     29: 
                     30:        /* copy sdots onto stack */
                     31:        p = a;
                     32:        do { *--q = p->I; p = p->CDR; } while (p);
                     33:        p = b;
                     34:        do { *--q = p->I; p = p->CDR; } while (p);
                     35:        while(q > base) *--q = 0;  /* initialize target */
                     36: 
                     37:        /* perform the multiplication */
                     38:        for(q = sb; q > sc; *--s = carry)
                     39:            for((r = sa, s = (q--) - lb, carry = 0); r > sb;)
                     40:            {
                     41:                    carry += *--s;
                     42:                    emul(*q,*--r,carry,&work);
                     43:                    test = work.low;
                     44:                    carry = work.high << 2;
                     45:                    if(test < 0) carry += 2;
                     46:                    if(test & 0x40000000) carry +=1;
                     47:                    *s = test & 0x3fffffff;
                     48:            }
                     49: 
                     50:        return(export(sc,base));
                     51: }

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