function count_chars( str, mode ) {	// Return information about characters used in a string
	// 
	// +   original by: Ates Goral (http://magnetiq.com)

	var histogram = new Object(), tmp_ar = new Array(), argc = arguments.length, key, i, code, mode;

	if (argc == 1) {
		mode = 0;
	}

	mode_even = (mode & 1) == 0;
	if (mode_even) {
		for (i = 1; i < 256; ++i) {
			histogram[i] = 0;
		}
	}

	for (i = 0; i < str.length; ++i) {
		code = str.charCodeAt(i);
		if (code in histogram) {
			++histogram[code];
		} else {
			histogram[code] = 1;
		}
	}

	if (mode > 0) {
		for (key in histogram) {
			if (histogram[key] == 0 != mode_even) {
				delete histogram[key];
			}
		}
	}

	if (mode < 3) {
		return histogram;
	} else {
		for (key in histogram) {
			tmp_ar.push(String.fromCharCode(key));
		}
		return tmp_ar.join("");
	}
}