C# Bitwise-or operator used on a sign-extended operand; consider casting to a smaller unsigned type first

问题

I know these warnings are probably pointless.. But anyway I could get rid of them?

I got 7 of these warnings.

Bitwise-or operator used on a sign-extended operand; consider casting to a smaller unsigned type first

This has something to do with the OR operator |

I highlighted what gives off the warnings.

int result = (int)ror((uint)(v76 ^ (v75 | 0x862D63D3)), (uint)(BitConverter.ToInt32(v4, 72) ^ 0x22));

int v11 = (int)rol((uint)(int)((v8 & v10 | ~v10 & 0xEFCDAAC9) + v3[2] - 1126481991), 17);

int v144 = (int)rol((uint)(int)((v141 & v143 | ~v143 & 0xEFCDAAC9) + v3[2] - 1126481991), 17);

int v77 = (int)(`BitConverter.ToInt32(v4, 52) | 0x96C35837`);


BitConverter.GetBytes((int)(v30 & 0x870DEA8A | v29)).CopyTo(v2, 32);

int temp24 |= (int)(BitConverter.ToInt32(v3, 48) | 0x96B4A1B4);

int v17 = (int)(BitConverter.ToInt32(v3, 12) | 0x83868A1D);

回答1:

A quick Web search shows the official documentation for the warning, which comes with an explanation:

The compiler implicitly widened and sign-extended a variable, and then used the resulting value in a bitwise OR operation. This can result in unexpected behavior.

The problem is that the expression v75 | 0x862D63D3 is of the form int | uint. This is computed by promoting both sides to long. If you really want sign extension, write (ulong)(long)v75 | 0x862D63D3. If you really want zero-extension, then write (uint)v75 |0x862D63D3.

class Program {
 public static void Main()
 {
  int v75 = int.MinValue;
  System.Console.WriteLine("{0:x}", v75 | 0x862D63D3);
  System.Console.WriteLine("{0:x}", (ulong)(long)v75 | 0x862D63D3);
  System.Console.WriteLine("{0:x}", (uint)v75 | 0x862D63D3);
 }
}

This program prints

ffffffff862d63d3
ffffffff862d63d3
862d63d3

As you can see, the compiler defaults to the first interpretation, which is probably not what you want.

回答2:

Try casting v75 and other variables being ORed with unsigned hex values to uint:

((uint)v75 | 0x862D63D3)

or declare the variables as uint instead of int.

回答3:

if you do OR operation for int and long variable, then system cast int to long. Exist two way for it :

namespace ConsoleApplication1
{
class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine($"int.MinValue  = {Convert.ToString(int.MinValue, 2)}");
        Console.WriteLine($"long.MinValue = {Convert.ToString(long.MinValue, 2)}");

        Console.WriteLine();

        long cast1 = int.MinValue;                   // !!!
        long cast2 = unchecked((uint)int.MinValue);  // !!!

        Console.WriteLine($"default cast = {Convert.ToString(cast1, 2)}");
        Console.WriteLine($"custom  cast = {Convert.ToString(cast2, 2)}");

        Console.WriteLine();

        Console.WriteLine($"default long OR int = {Convert.ToString(long.MinValue | int.MinValue, 2)}");
        Console.WriteLine($"custom  long OR int = {Convert.ToString(long.MinValue | unchecked((uint)int.MinValue), 2)}");
}
}

Result:

int.MinValue  = 10000000000000000000000000000000
long.MinValue = 1000000000000000000000000000000000000000000000000000000000000000

default cast = 1111111111111111111111111111111110000000000000000000000000000000
custom  cast = 0000000000000000000000000000000010000000000000000000000000000000

default long OR int = 1111111111111111111111111111111110000000000000000000000000000000
custom  long OR int = 1000000000000000000000000000000010000000000000000000000000000000

How result you want?

来源：https://stackoverflow.com/questions/7328052/c-sharp-bitwise-or-operator-used-on-a-sign-extended-operand-consider-casting-to

标签

bit-manipulation

compiler-warnings

suppress-warnings