C#•10mo ago

Casting from int to uint and back

Is casting a negative int to a uint and then back to a int guaranteed to give back the original negative value on all platforms, architectures and runtimes? Thanks!

8 Replies

MODiX•10mo ago

Angius

REPL Result: Failure

(uint)-17

(uint)-17

Exception: CompilationErrorException

- Constant value '-17' cannot be converted to a 'uint' (use 'unchecked' syntax to override)

- Constant value '-17' cannot be converted to a 'uint' (use 'unchecked' syntax to override)

Compile: 190.472ms | Execution: 0.000ms | React with ❌ to remove this embed.

Angius•10mo ago

You can't cast it

jcotton42•10mo ago

@ZZZZZZZZZZZZZZZZZZZZZZZZZ that's only an issue for literals pretty sure uh modix? you showed the result for a split second?

Angius•10mo ago

I saw that too lol

jcotton42•10mo ago

https://sharplab.io/#v2:C4LgTgrgdgNAJiA1AHwAICYAMBYAUBgRjzwEspgACEigXgoFoCB2AbjwjMolooAoPyAShJtcnKuh69OgiKLyoCATmmDRilRDULl09GqA @ZZZZZZZZZZZZZZZZZZZZZZZZZ @ikalou.

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jcotton42•10mo ago

in any case, in an unchecked context (the default) it's just a reinterpret cast so the underlying bits remain the same

MODiX•10mo ago

jcotton42

REPL Result: Success

int i = -17;
uint u = (uint)i;
int i2 = (int)u;

Console.WriteLine(i);
Console.WriteLine(u);
Console.WriteLine(i2);

int i = -17;
uint u = (uint)i;
int i2 = (int)u;

Console.WriteLine(i);
Console.WriteLine(u);
Console.WriteLine(i2);

Console Output

-17
4294967279
-17

-17
4294967279
-17

Compile: 356.110ms | Execution: 68.280ms | React with ❌ to remove this embed.

ikalou.OP•10mo ago

Thanks everyone! Yes I tested it on my machine but I wanted to make sure I could rely on it the result wasn't undefined / an implementation detail.

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Casting from int to uint and back