Use AsLargeInt to: 

Assign the large integer field value to a 64-bit integer variable. 

Assign a 64-bit integer value to the large integer field. 

For example, this code assigns a 64-bit integer value to a large integer field:

MyLargeIntegerField.AsLargeInt := 2147483648;

MyLargeIntegerField->AsLargeInt = 2147483648;

To assign a large integer field value to a 64-bit integer, use code similar to this:

LargeIntegerVariable := MyLargeIntegerField.AsLargeInt;

LargeIntVariable = MyLargeIntegerField->AsLargeInt;

If a value assigned to the field is not within the range established by the MinValue and MaxValue properties, an EDatabaseError exception is raised. 

Value 

MaxValue 

MinValue