4.3BSD - /usr/src/new/icon/operators/swap.c

   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)

Defined functions