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Annotation of 43BSD/contrib/icon/operators/swap.c, revision 1.1

1.1     ! root        1: #include "../h/rt.h"
        !             2: 
        !             3: /*
        !             4:  * x :=: y - swap values of x and y.
        !             5:  */
        !             6: 
        !             7: swap(nargs, arg2v, arg2, arg1, arg0)
        !             8: int nargs;
        !             9: struct descrip arg2v, arg2, arg1, arg0;
        !            10:    {
        !            11:    register union block *bp1, *bp2;
        !            12:    int adj1, adj2;
        !            13: 
        !            14:    SetBound;
        !            15:    /*
        !            16:     * x and y must be variables.
        !            17:     */
        !            18:    if (QUAL(arg1) || !VAR(arg1))
        !            19:       runerr(111, &arg1);
        !            20:    if (QUAL(arg2) || !VAR(arg2))
        !            21:       runerr(111, &arg2);
        !            22:    /*
        !            23:     * Make copies of x and y as variables in arg0 and arg2v.
        !            24:     */
        !            25:    arg0 = arg1;
        !            26:    arg2v = arg2;
        !            27:    adj1 = adj2 = 0;
        !            28:    if (arg1.type == D_TVSUBS && arg2.type == D_TVSUBS) {
        !            29:       bp1 = BLKLOC(arg1);
        !            30:       bp2 = BLKLOC(arg2);
        !            31:       if (VARLOC(bp1->tvsubs.ssvar) == VARLOC(bp2->tvsubs.ssvar)) {
        !            32:          /*
        !            33:          * x and y are both substrings of the same string, set
        !            34:          *  adj1 and adj2 for use in locating the substrings after
        !            35:          *  an assignment has been made.  If x is to the right of y,
        !            36:          *  set adj1 := *x - *y, otherwise if y is to the right of x,
        !            37:          *  set adj2 := *y - *x.  Note that the adjustment values may
        !            38:          *  be negative.
        !            39:          */
        !            40:          if (bp1->tvsubs.sspos > bp2->tvsubs.sspos)
        !            41:             adj1 = bp1->tvsubs.sslen - bp2->tvsubs.sslen;
        !            42:          else if (bp2->tvsubs.sspos > bp1->tvsubs.sspos)
        !            43:             adj2 = bp2->tvsubs.sslen - bp1->tvsubs.sslen;
        !            44:         }
        !            45:       }
        !            46:    DeRef(arg1)
        !            47:    DeRef(arg2)
        !            48:    /*
        !            49:     * Do x := y
        !            50:     */
        !            51:    doasgn(&arg0, &arg2);
        !            52:    if (adj2 != 0)
        !            53:       /*
        !            54:        * y is to the right of x and the assignment x := y has shifted
        !            55:        *  the position of y.  Add adj2 to the position of y to account
        !            56:        *  for the replacement of x by y.
        !            57:        */
        !            58:       BLKLOC(arg2)->tvsubs.sspos += adj2;
        !            59:    /*
        !            60:     * Do y := x
        !            61:     */
        !            62:    doasgn(&arg2v, &arg1);
        !            63:    if (adj1 != 0)
        !            64:       /*
        !            65:        * x is to the right of y and the assignment y := x has shifted
        !            66:        *  the position of x.  Add adj2 to the position of x to account
        !            67:        *  for the replacement of y by x.
        !            68:        */
        !            69:       BLKLOC(arg1)->tvsubs.sspos += adj1;
        !            70:    ClearBound;
        !            71:    }
        !            72: 
        !            73: Opblockx(swap,3,":=:",2)

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