count

/*
 *  call-seq:
 *     str.count([other_str]+)   => fixnum
 *  
 *  Each <i>other_str</i> parameter defines a set of characters to count.  The
 *  intersection of these sets defines the characters to count in
 *  <i>str</i>. Any <i>other_str</i> that starts with a caret (^) is
 *  negated. The sequence c1--c2 means all characters between c1 and c2.
 *     
 *     a = "hello world"
 *     a.count "lo"            #=> 5
 *     a.count "lo", "o"       #=> 2
 *     a.count "hello", "^l"   #=> 4
 *     a.count "ej-m"          #=> 4
 */

static VALUE
rb_str_count(argc, argv, str)
    int argc;
    VALUE *argv;
    VALUE str;
{
    char table[256];
    char *s, *send;
    int init = 1;
    int i;

    if (argc < 1) {
        rb_raise(rb_eArgError, "wrong number of arguments");
    }
    for (i=0; i<argc; i++) {
        VALUE s = argv[i];

        StringValue(s);
        tr_setup_table(s, table, init);
        init = 0;
    }

    s = RSTRING(str)->ptr;
    if (!s || RSTRING(str)->len == 0) return INT2FIX(0);
    send = s + RSTRING(str)->len;
    i = 0;
    while (s < send) {
        if (table[*s++ & 0xff]) {
            i++;
        }
    }
    return INT2NUM(i);
}