Casting from int to uint and back

ikalou. · 2024-02-08T21:50:21.244Z

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!

M

MODiX•2/8/24, 9:57 PM

Angius

REPL Result: Failure

(uint)-17

(uint)-17

(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)

- 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.

A

Angius•2/8/24, 9:57 PM

You can't cast it

J

jcotton42•2/8/24, 10:05 PM

@ZZZZZZZZZZZZZZZZZZZZZZZZZ that's only an issue for literals pretty sure

J

jcotton42•2/8/24, 10:06 PM

uh modix?
you showed the result for a split second?

A

Angius•2/8/24, 10:07 PM

I saw that too lol

J

jcotton42•2/8/24, 10:07 PM

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

SharpLab

C#/VB/F# compiler playground.

J

jcotton42•2/8/24, 10:08 PM

in any case, in an

unchecked

unchecked

unchecked

unchecked context (the default) it's just a reinterpret cast

J

jcotton42•2/8/24, 10:08 PM

so the underlying bits remain the same

M

MODiX•2/8/24, 10:09 PM

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);

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

-17
4294967279
-17

-17
4294967279
-17

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

I

ikalou.OP•2/8/24, 10:11 PM

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.