presto-iceberg/src/main/java/io/prestosql/plugin/iceberg/PartitionTransforms.java/PartitionTransforms/extractTimestamp
class PartitionTransforms:    private static Block extractTimestamp(Block block, LongUnaryOperator function)
    {
        BlockBuilder builder = INTEGER.createFixedSizeBlockBuilder(block.getPositionCount());
        for (int position = 0; position < block.getPositionCount(); position++) {
            if (block.isNull(position)) {
                builder.appendNull();
                continue;
            }
            long value = TIMESTAMP.getLong(block, position);
            value = function.applyAsLong(value);
            INTEGER.writeLong(builder, value);
        }
        return builder.build();
    }