Bitwise rotate left function

Question

I am trying to implement a rotate left function that rotates an integer x left by n bits

• Ex: rotateLeft(0x87654321,4) = 0x76543218
• Legal ops: ~ &

Answer 1

The best way is:

int rotateLeft(int x, int n)
{
    _asm
    {
        mov eax, dword ptr [x]
        mov ecx, dword ptr [n]
        rol eax, cl
    }
}

If you need to rotate an int variable right in your code, then the fastest way is:

#define rotl( val, shift ) _asm mov eax, dword ptr[val] _asm mov ecx, dword ptr [shift] _asm rol eax, cl _asm mov dword ptr [val], eax

val is the value you rotate, shift is the length of the rotation.