C++ Gray code

gray.cc

//
// Code from "Numerical Recipe in C (2nd edition)" by Press et al. 
// Chapter 20.2 pg.896
// 

#include <cstdint>
#include <iostream>

// Return the Gray code of n
uint64_t gray(uint64_t n)
{
    // This is the easy direction!
    return (n ^ (n >> 1));
}

// Return the inverse Gray code of n
uint64_t inverse_gray(uint64_t n)
{
    // This is the more complicated direction: In hierarchical 
    // stages, starting with a one-bit right shift, cause each 
    // bit to be XORed with all more significant bits.
    int ish = 1;
    uint64_t ans = n;
    uint64_t idiv = 0;
    
    for (;;) {
        idiv = (ans >> ish);
        ans ^= idiv;
        if (idiv <= 1 || ish == 16)
            return ans;
        ish <<= 1;
    }
    return ans;
}
 
int main ()
{
    for (int i = 0; i < 64; i++) {
        // Convert i to Gray code, and then convert it back
        std::cout << i << " " << gray(i) << " " << inverse_gray(gray(i)) << std::endl;
    }
}