feat(iceberg): Add timestamp_ns function

Author: Joe-Abraham

velox/functions/iceberg/DateTimeFunctions.cpp

@@ -87,6 +87,19 @@ struct HoursFunction {
   }
 };
 
+// timestamp_ns(input) -> nanoseconds from 1970-01-01 00:00:00.000000000
+// Input is timestamp.
+template <typename TExec>
+struct TimestampNsFunction {
+  VELOX_DEFINE_FUNCTION_TYPES(TExec);
+
+  FOLLY_ALWAYS_INLINE void call(
+      int64_t& result,
+      const arg_type<Timestamp>& timestamp) {
+    result = epochNanos(timestamp);
+  }
+};
+
 void registerDateTimeFunctions(const std::string& prefix) {
   registerFunction<YearsFunction, int32_t, Timestamp>({prefix + "years"});
   registerFunction<YearsFunction, int32_t, Date>({prefix + "years"});
@@ -95,6 +108,8 @@ void registerDateTimeFunctions(const std::string& prefix) {
   registerFunction<DaysFunction, Date, Timestamp>({prefix + "days"});
   registerFunction<DaysFunction, Date, Date>({prefix + "days"});
   registerFunction<HoursFunction, int32_t, Timestamp>({prefix + "hours"});
+  registerFunction<TimestampNsFunction, int64_t, Timestamp>(
+      {prefix + "timestamp_ns"});
 }
 
 } // namespace facebook::velox::functions::iceberg

velox/functions/iceberg/DateTimeUtil.h

@@ -54,4 +54,10 @@ FOLLY_ALWAYS_INLINE int32_t epochHour(Timestamp ts) {
   return (seconds >= 0) ? seconds / 3'600 : ((seconds + 1) / 3'600) - 1;
 }
 
+/// Extract nanoseconds from 1970-01-01 00:00:00.000000000.
+/// Stores nanoseconds from 1970-01-01 00:00:00.000000000.
+FOLLY_ALWAYS_INLINE int64_t epochNanos(Timestamp ts) {
+  return ts.getSeconds() * 1'000'000'000L + ts.getNanos();
+}
+
 } // namespace facebook::velox::functions::iceberg

velox/functions/iceberg/tests/DateTimeFunctionsTest.cpp

@@ -84,5 +84,25 @@ TEST_F(DateTimeFunctionsTest, hours) {
   EXPECT_EQ(-1, hours("1969-12-31 23:59:58.999999"));
 }
 
+TEST_F(DateTimeFunctionsTest, timestampNs) {
+  const auto timestampNs = [&](const std::string& ts) {
+    return evaluateOnce<int64_t>(
+        "timestamp_ns(c0)", std::make_optional<Timestamp>(parseTimestamp(ts)));
+  };
+
+  // 1970-01-01 00:00:00.000000000 should be 0
+  EXPECT_EQ(0, timestampNs("1970-01-01 00:00:00.000000"));
+
+  // 2017-12-01 10:12:55.038194 is 1512123175038194000 nanoseconds from
+  // 1970-01-01
+  EXPECT_EQ(1512123175038194000L, timestampNs("2017-12-01 10:12:55.038194"));
+
+  // 1970-01-01 00:00:01.000001 is 1000001000 nanoseconds from 1970-01-01
+  EXPECT_EQ(1000001000L, timestampNs("1970-01-01 00:00:01.000001"));
+
+  // Timestamp before 1970 should be negative
+  EXPECT_EQ(-1000000000L, timestampNs("1969-12-31 23:59:59.000000"));
+}
+
 } // namespace
 } // namespace facebook::velox::functions::iceberg