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Annotation of 43BSD/ucb/lisp/franz/68k/mulbig.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * $Header: mulbig.c,v 1.2 83/11/26 12:13:29 sklower Exp $
        !             3:  * $Locker:  $
        !             4:  *
        !             5:  * Copyright (c) 1982, Regents, University of California
        !             6:  *
        !             7:  */
        !             8: 
        !             9: #include "global.h"
        !            10: 
        !            11: struct s_dot   { long I; struct s_dot *CDR; };
        !            12: struct vl      { long high; long low; };
        !            13: 
        !            14: struct s_dot *mulbig(a,b)
        !            15: struct s_dot *a, *b;
        !            16: {
        !            17:        int la = 1, lb = 1;
        !            18:        long *sa, *sb, *sc, *base, *alloca();
        !            19:        struct s_dot *export();
        !            20:        register struct s_dot *p;
        !            21:        register int *q, *r, *s;
        !            22:        long carry = 0, test;
        !            23:        struct vl work;
        !            24:        Keepxs();
        !            25: 
        !            26:        /* compute lengths */
        !            27:        
        !            28:        for(p = a; p->CDR; p = p->CDR) la++;
        !            29:        for(p = b; p->CDR; p = p->CDR) lb++;
        !            30: 
        !            31:        /* allocate storage areas on the stack */
        !            32: 
        !            33:        base = alloca((la + la + lb + lb + 1)*sizeof(long));
        !            34:        sc = base + la + lb + 1;
        !            35:        sb = sc + lb;
        !            36:        sa = sb + la;
        !            37:        q  = sa;
        !            38: 
        !            39:        /* copy s_dots onto stack */
        !            40:        p = a;
        !            41:        do { *--q = p->I; p = p->CDR; } while (p);
        !            42:        p = b;
        !            43:        do { *--q = p->I; p = p->CDR; } while (p);
        !            44:        while(q > base) *--q = 0;  /* initialize target */
        !            45: 
        !            46:        /* perform the multiplication */
        !            47:        for(q = sb; q > sc; *--s = carry)
        !            48:            for((r = sa, s = (q--) - lb, carry = 0); r > sb;)
        !            49:            {
        !            50:                    carry += *--s;
        !            51:                    emul(*q,*--r,carry,&work);
        !            52:                    test = work.low;
        !            53:                    carry = work.high << 2;
        !            54:                    if(test < 0) carry += 2;
        !            55:                    if(test & 0x40000000) carry +=1;
        !            56:                    *s = test & 0x3fffffff;
        !            57:            }
        !            58: 
        !            59:        p = export(sc,base);
        !            60:        Freexs();
        !            61:        return(p);
        !            62: }

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