What's the fastest way to divide an integer by 3?

This is the fastest as the compiler will optimize it if it can depending on the output processor.

int a;
int b;

a = some value;
b = a / 3;

A lookup table approach would also be faster in some architectures.

uint8_t DivBy3LU(uint8_t u8Operand)
{
   uint8_t ai8Div3 = [0, 0, 0, 1, 1, 1, 2, 2, 2, 3, 3, 3, 4, ....];

   return ai8Div3[u8Operand];
}