Q re integer multiply

I noticed that when I multiply two integer(4) quantities together,

the compiler does not allow the result to be integer(8).

So is there a way to FORCE the correct answer?

For example:

integer(4) x,y

integer(8) z

Z=x*y does not give correct results in MOST cases, unless x and y are small.

What can I do to MAKE SURE I will get the correct answer?

Notice that if x and y are each 31 bits, Z can be 62 bits, which will fit into a INTEGER(8) result.

Is there a way to force the compiler to look for an integer overflow?