jodd-core/src/main/java/jodd/util/MathUtil.java
public static int parseDigit(final char digit) {
		if ((digit >= '0') && (digit <= '9')) {
			return digit - '0';
		}
		if (CharUtil.isLowercaseAlpha(digit)) {
			return 10 + digit - 'a';
		}
		return 10 + digit - 'A';
	}
public static int parseDigit(final char digit) {
		if ((digit >= '0') && (digit <= '9')) {
			return digit - '0';
		}
		if (CharUtil.isLowercaseAlpha(digit)) {
			return 10 + digit - 'a';
		}
		return 10 + digit - 'A';
	}
Converts char digit into integer value.
Accepts numeric chars (0 - 9) as well as letter (A-z).