generates a graycode (recently edited to be simpler, faster, stronger...)

graycode.c

#include <stdio.h>
#include <math.h>
#include <string.h>
#include <stdlib.h>

void print_bin(int iteration, int value)
{
    char buffer[36];
    memset(buffer, 0, sizeof(buffer));
    
    for (int i = 0; i < 32; ++i) {
        int bit = value & (1 << (31 - i));
        buffer[i] = (char)0x30 + (char)!!bit;
    }
    
    printf("[%i] 0b%s = %i\n", iteration, buffer, value);
}

static void graycode(int *codes, int n)
{    
    int len = 1 << n;
    
    for (int bit = 0; bit < n; ++bit) {
        int period = (1 << (bit + 1)) - 1;
        int parity = 0;
        int counter = 0;
        int p = 1 << bit;
        
        for (int i = p; i < len; ++i) {
            if ((counter & period) == 0) {
                parity ^= p;
            }
            
            codes[i] ^= parity;
            
            counter++;
        }
    }
}

int main(int argc, const char * argv[]) 
{    
    const int N = 16;
    
    int *codes = calloc(1 << N, sizeof(*codes));
    
    graycode(codes, N);
    
    int len = 1 << N;
    
    for (int i = 0; i < len; ++i) {
        print_bin(i, codes[i]);
    }
    
    puts("Running dupe check.");
    for (int i = 0; i < len; ++i) {
        for (int j = 0; j < len; ++j) {
            if (j != i && codes[i] == codes[j]) {
                printf("Dupe: [%i] ", i);
                print_bin(j, codes[j]);
            }
        } 
    } 
    
    puts("Running count check.");
    for (int i = 0; i < len; ++i) {
        int found = 0;
        for (int j = 0; j < len && !found; ++j) {
            if (codes[j] == i)
                found = 1;
        }
        
        if (!found) {
            printf("Could not find %i!\n", i);
        }
    }
    
    puts("Running bit comparison check.");
    for (int i = 0; i < (len - 1); ++i) {
        int diff_count = 0;
        for (int k = 0; k < N; ++k) {
            int b0 = codes[i] & (1 << k);
            int b1 = codes[i + 1] & (1 << k);
            if (b0 != b1) {
                diff_count++;
            }
        }
        if (diff_count > 1) {
            printf("(%i, %i) differ by more than one bit!\n", i, i + 1);
        }
    }
    
    free(codes);
    
    return 0;
}