presto-main/src/main/java/io/prestosql/operator/scalar/StringFunctions.java/StringFunctions/hammingDistance
class StringFunctions:    @Description("computes Hamming distance between two strings")
    @ScalarFunction
    @LiteralParameters({"x", "y"})
    @SqlType(StandardTypes.BIGINT)
    public static long hammingDistance(@SqlType("varchar(x)") Slice left, @SqlType("varchar(y)") Slice right)
    {
        int distance = 0;
        int leftPosition = 0;
        int rightPosition = 0;
        while (leftPosition < left.length() && rightPosition < right.length()) {
            int codePointLeft = tryGetCodePointAt(left, leftPosition);
            int codePointRight = tryGetCodePointAt(right, rightPosition);

            // if both code points are invalid, we do not care if they are equal
            // the following code treats them as equal if they happen to be of the same length
            if (codePointLeft != codePointRight) {
                distance++;
            }

            leftPosition += codePointLeft > 0 ? lengthOfCodePoint(codePointLeft) : -codePointLeft;
            rightPosition += codePointRight > 0 ? lengthOfCodePoint(codePointRight) : -codePointRight;
        }

        checkCondition(
                leftPosition == left.length() && rightPosition == right.length(),
                INVALID_FUNCTION_ARGUMENT,
                "The input strings to hamming_distance function must have the same length");

        return distance;
    }