4.3BSD - /usr/src/new/icon/functions/bal.c

   1: #include "../h/rt.h"
   2: 
   3: /*
   4:  * bal(c1,c2,c3,s,i,j) - find end of a balanced substring of s[i:j].
   5:  *  Generates successive positions.
   6:  */
   7: 
   8: Xbal(nargs, arg6, arg5, arg4, arg3, arg2, arg1, arg0)
   9: int nargs;
  10: struct descrip arg6, arg5, arg4, arg3, arg2, arg1, arg0;
  11:    {
  12:    register int i, j, cnt;
  13:    register c;
  14:    int t;
  15:    long l1, l2;
  16:    int *cs1, *cs2, *cs3;
  17:    int csbuf1[CSETSIZE], csbuf2[CSETSIZE], csbuf3[CSETSIZE];
  18:    char sbuf[MAXSTRING];
  19:    static int lpar[CSETSIZE] =  /* '(' */
  20:       cset_display(0, 0, 0400, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0);
  21:    static int rpar[CSETSIZE] =  /* ')' */
  22:       cset_display(0, 0, 01000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0);
  23: 
  24:    /*
  25:     *  c1 defaults to &cset; c2 defaults to '(' (lpar); c3 defaults to
  26:     *   ')' (rpar); s to &subject; i to &pos if s defaulted, 1 otherwise;
  27:     *   j defaults to 0.
  28:     */
  29:    defcset(&arg1, &cs1, csbuf1, k_cset.bits);
  30:    defcset(&arg2, &cs2, csbuf2, lpar);
  31:    defcset(&arg3, &cs3, csbuf3, rpar);
  32:    if (defstr(&arg4, sbuf, &k_subject))
  33:       defint(&arg5, &l1, k_pos);
  34:    else
  35:       defint(&arg5, &l1, 1);
  36:    defint(&arg6, &l2, 0);
  37: 
  38:    /*
  39:     * Convert i and j to positions in s and order them.
  40:     */
  41:    i = cvpos(l1, STRLEN(arg4));
  42:    j = cvpos(l2, STRLEN(arg4));
  43:    if (i > j) {
  44:       t = i;
  45:       i = j;
  46:       j = t;
  47:       }
  48: 
  49:    /*
  50:     * Loop through characters in s[i:j].  When a character in cs2 is
  51:     *  found, increment cnt; when a chracter in cs3 is found, decrement
  52:     *  cnt.  When cnt is 0 there have been an equal number of occurrences
  53:     *  of characters in cs2 and cs3, i.e., the string to the left of
  54:     *  i is balanced.  If the string is balanced and the current character
  55:     *  (s[i]) is in c1, suspend i.  Note that if cnt drops below zero,
  56:     *  bal fails.
  57:     */
  58:    cnt = 0;
  59:    while (i < j) {
  60:       c = STRLOC(arg4)[i-1];
  61:       if (cnt == 0 && tstb(c, cs1)) {
  62:          arg0.type = D_INTEGER;
  63:          INTVAL(arg0) = i;
  64:          suspend();
  65:          }
  66:       if (tstb(c, cs2))
  67:          cnt++;
  68:       else if (tstb(c, cs3))
  69:          cnt--;
  70:       if (cnt < 0)
  71:          fail();
  72:       i++;
  73:       }
  74:    /*
  75:     * Eventually fail.
  76:     */
  77:    fail();
  78:    }
  79: 
  80: Procblock(bal,6)

Defined functions