CODEWITHSUNDEEP
.net64-bitmathinteger-overflowint64
Brann
Brann

Reputation: 32376

Why do my .net Int64's behaves as if they were Int32's?

I'm witnessing a strange behavior in a .net program :

Console.WriteLine(Int64.MaxValue.ToString());
// displays 9223372036854775807, which is 2^63-1, as expected

Int64 a = 256*256*256*127; // ok

Int64 a = 256*256*256*128; // compile time error : 
//"The operation overflows at compile time in checked mode"
// If i do this at runtime, I get some negative values, so the overflow indeed happens.

Why do my Int64's behaves as if they were Int32's, although Int64.MaxValue seems to confirm they're using 64 bits ?

If it's relevant, I'm using a 32 bit OS, and the target platform is set to "Any CPU"

Upvotes: 7

Views: 720

Answers (2)

Pop Catalin
Pop Catalin

Reputation: 62940

Use:

Int64 a = 256L*256L*256L*128L;

the L suffix means Int64 literal, no suffix means Int32.

What your wrote:

Int64 a = 256*256*256*128

means:

Int64 a = (Int32)256*(Int32)256*(Int32)256*(Int32)128;

Upvotes: 4

Jon Skeet
Jon Skeet

Reputation: 1500385

Your RHS is only using Int32 values, so the whole operation is performed using Int32 arithmetic, then the Int32 result is promoted to a long.

Change it to this:

Int64 a = 256*256*256*128L;

and all will be well.

Upvotes: 20

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