lstrip!

/*
 *  call-seq:
 *     str.lstrip!   => self or nil
 *  
 *  Removes leading whitespace from <i>str</i>, returning <code>nil</code> if no
 *  change was made. See also <code>String#rstrip!</code> and
 *  <code>String#strip!</code>.
 *     
 *     "  hello  ".lstrip   #=> "hello  "
 *     "hello".lstrip!      #=> nil
 */

static VALUE
rb_str_lstrip_bang(str)
    VALUE str;
{
    char *s, *t, *e;

    s = RSTRING(str)->ptr;
    if (!s || RSTRING(str)->len == 0) return Qnil;
    e = t = s + RSTRING(str)->len;
    /* remove spaces at head */
    while (s < t && ISSPACE(*s)) s++;

    if (s > RSTRING(str)->ptr) {
        rb_str_modify(str);
        RSTRING(str)->len = t-s;
        memmove(RSTRING(str)->ptr, s, RSTRING(str)->len);
        RSTRING(str)->ptr[RSTRING(str)->len] = '\0';
        return str;
    }
    return Qnil;
}