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Annotation of 43BSDTahoe/ucb/lisp/franz/tahoe/adbig.c, revision 1.1

1.1     ! root        1: /*
        !             2:  *
        !             3:  * Copyright (c) 1982, Regents, University of California
        !             4:  *
        !             5:  * stolen from 68k port by P. S. Housel 05/03/86
        !             6:  */
        !             7: #include "global.h"
        !             8: 
        !             9: struct s_dot
        !            10:        {
        !            11:         long I;
        !            12:        struct s_dot *CDR;
        !            13:        };
        !            14: struct vl
        !            15:        {
        !            16:         long high;
        !            17:         long low;
        !            18:        };
        !            19: 
        !            20: 
        !            21: struct s_dot *adbig(a,b)
        !            22: struct s_dot *a, *b;
        !            23: {
        !            24:        int la = 1, lb = 1;
        !            25:        long *sa, *sb, *sc, *base, *alloca();
        !            26:        struct s_dot *export();
        !            27:        register struct s_dot *p;
        !            28:        register int *q, *r, *s;
        !            29:        register carry = 0;
        !            30:        Keepxs();
        !            31: 
        !            32:        /* compute lengths */
        !            33:        
        !            34:        for(p = a; p->CDR; p = p->CDR) la++;
        !            35:        for(p = b; p->CDR; p = p->CDR) lb++;
        !            36:        if(lb > la) la = lb;
        !            37: 
        !            38:        /* allocate storage areas on the stack */
        !            39: 
        !            40:        base = alloca((3*la+1)*sizeof(long));
        !            41:        sc = base + la +1;
        !            42:        sb = sc + la;
        !            43:        sa = sb + la;
        !            44:        q  = sa;
        !            45: 
        !            46:        /* copy s_dots onto stack */
        !            47:        p = a;
        !            48:        do { *--q = p->I; p = p->CDR; } while (p);
        !            49:        while(q > sb) *--q = 0;
        !            50:        p = b;
        !            51:        do { *--q = p->I; p = p->CDR; } while (p);
        !            52:        while(q > sc) *--q = 0;
        !            53: 
        !            54:        /* perform the addition */
        !            55:        for(q = sa, r = sb, s = sc; q > sb;)
        !            56:        {
        !            57:                carry += *--q + *--r;
        !            58:                *--s = carry & 0x3fffffff;
        !            59:                carry >>= 30;
        !            60:        }
        !            61:        *--s = carry;
        !            62: 
        !            63:        p = export(sc,base);
        !            64:        Freexs();
        !            65:        return(p);
        !            66: }

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