Add luhn_check function

presto-docs/src/main/sphinx/functions/string.rst

@@ -81,6 +81,11 @@ String Functions
 
     Removes leading whitespace from ``string``.
 
+.. function:: luhn_check(string) -> boolean
+
+    Tests whether a ``string`` of digits is valid according to the
+    `Luhn algorithm <https://en.wikipedia.org/wiki/Luhn_algorithm>`_.
+
 .. function:: position(substring IN string) -> bigint
 
     Returns the starting position of the first instance of ``substring`` in

presto-main/src/main/java/io/prestosql/metadata/FunctionRegistry.java

@@ -114,6 +114,7 @@
 import io.prestosql.operator.scalar.JoniRegexpReplaceLambdaFunction;
 import io.prestosql.operator.scalar.JsonFunctions;
 import io.prestosql.operator.scalar.JsonOperators;
+import io.prestosql.operator.scalar.LuhnCheckFunction;
 import io.prestosql.operator.scalar.MapCardinalityFunction;
 import io.prestosql.operator.scalar.MapDistinctFromOperator;
 import io.prestosql.operator.scalar.MapEntriesFunction;
@@ -537,6 +538,7 @@ public FunctionRegistry(Metadata metadata, FeaturesConfig featuresConfig)
                 .scalars(JoniRegexpCasts.class)
                 .scalars(CharacterStringCasts.class)
                 .scalars(CharOperators.class)
+                .scalars(LuhnCheckFunction.class)
                 .scalar(CharOperators.CharDistinctFromOperator.class)
                 .scalar(DecimalOperators.Negation.class)
                 .scalar(DecimalOperators.HashCode.class)

presto-main/src/main/java/io/prestosql/operator/scalar/LuhnCheckFunction.java

@@ -0,0 +1,66 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package io.prestosql.operator.scalar;
+
+import io.airlift.slice.Slice;
+import io.prestosql.spi.function.Description;
+import io.prestosql.spi.function.ScalarFunction;
+import io.prestosql.spi.function.SqlType;
+import io.prestosql.spi.type.StandardTypes;
+
+import static io.prestosql.spi.StandardErrorCode.INVALID_FUNCTION_ARGUMENT;
+import static io.prestosql.util.Failures.checkCondition;
+
+public final class LuhnCheckFunction
+{
+    private LuhnCheckFunction() {}
+
+    @Description("Checks that a string of digits is valid according to the Luhn algorithm")
+    @ScalarFunction("luhn_check")
+    @SqlType(StandardTypes.BOOLEAN)
+    public static boolean LuhnCheck(@SqlType(StandardTypes.VARCHAR) Slice slice)
+    {
+        if (slice.length() == 0) {
+            return false;
+        }
+
+        int nDigits = slice.length();
+        int sum = 0;
+        boolean secondNumber = false;
+
+        for (int i = nDigits - 1; i >= 0; i--) {
+            byte b = slice.getByte(i);
+            checkCondition(b >= '0' && b <= '9', INVALID_FUNCTION_ARGUMENT, "Input contains non-digit character");
+            int n = b - '0';
+
+            // starting from the right double the value of every other number
+            if (secondNumber) {
+                n *= 2;
+            }
+
+            // if the value is greater than 9 subtract 9 from n
+            if (n > 9) {
+                n -= 9;
+            }
+
+            // add to sum
+            sum += n;
+
+            // update second number check
+            secondNumber = !secondNumber;
+        }
+        //check returns true if mod 10 is zero
+        return (sum % 10 == 0);
+    }
+}

presto-main/src/test/java/io/prestosql/operator/scalar/TestLuhnCheckFunction.java

@@ -0,0 +1,36 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package io.prestosql.operator.scalar;
+
+import org.testng.annotations.Test;
+
+import static io.prestosql.spi.StandardErrorCode.INVALID_FUNCTION_ARGUMENT;
+import static io.prestosql.spi.type.BooleanType.BOOLEAN;
+
+public class TestLuhnCheckFunction
+        extends AbstractTestFunctions
+{
+    @Test
+    public void testLuhnCheck()
+    {
+        assertFunction("luhn_check('4242424242424242')", BOOLEAN, true);
+        assertFunction("luhn_check('1234567891234567')", BOOLEAN, false);
+        assertFunction("luhn_check('')", BOOLEAN, false);
+        assertFunction("luhn_check(NULL)", BOOLEAN, null);
+        assertInvalidFunction("luhn_check('abcd424242424242')", INVALID_FUNCTION_ARGUMENT);
+        assertFunction("luhn_check('123456789')", BOOLEAN, false);
+        assertInvalidFunction("luhn_check('\u4EA0\u4EFF\u4EA112345')", INVALID_FUNCTION_ARGUMENT);
+        assertInvalidFunction("luhn_check('4242\u4FE124242424242')", INVALID_FUNCTION_ARGUMENT);
+    }
+}