hamming

#include <stdio.h>
#include <stdint.h>
#include <limits.h>

#define BUFFER_SIZE (4096 * sizeof(char))
#define INT32_BIT (CHAR_BIT * sizeof(int32_t))
#define IS_POW2(x) ((x & (x - 1)) == 0)

uint32_t hamming_encode(const char *src, char *dst, size_t dst_size)
{
    uint32_t result = 0; // 0 - success
    char *ctrl[INT32_BIT], curc, *dst_end = dst + dst_size;
    uint32_t i = 1, q = 0, k = 0;
    while(dst < dst_end)
    {
        if (!IS_POW2(i))
        {
            if ((curc = *src) == '\0') break;
            ++src;
            if (curc == '1' || curc == '0')
            {
                if (curc == '1') q ^= i;
                *dst = curc;
            }
            else continue; // ignore invalid symbols
        }
        else ctrl[k++] = dst;
        ++i;
        ++dst;
    }
    for (i = 0; i < k; ++i)
    {
        *ctrl[i] = (q & 1) + '0';
        q >>= 1;
    }
    *dst = '\0';
    if (*src != '\0') result = 1; // 1 - output buffer is small
    return result;
}

uint32_t hamming_check(const char *str)
{
    uint32_t i = 1, q = 0;
    for (; *str != '\0'; ++str, ++i)
    {
        if (*str == '1') q ^= i;
    }
    return q; // 0 - success, no errors
}

void hamming_decode(char *str)
{
    uint32_t i = 1;
    char *dst = str;
    for (; *str != '\0'; ++str, ++i)
    {
        if (!IS_POW2(i)) *dst++ = *str;
    }
    *dst = '\0';
}

int main()
{
    // const char *src = "1110000100";
    char src[BUFFER_SIZE];
    char dst[BUFFER_SIZE];
    uint32_t error_code;
    printf("Enter bit-string to hamming encode/decode:\n");
    fgets(src, BUFFER_SIZE, stdin);
    if ((error_code = hamming_encode(src, dst, BUFFER_SIZE)) == 0)
    {
        printf("%s\n", dst);
        if ((error_code = hamming_check(dst)) == 0)
        {
            printf("Hamming code is valid. Decode...\n");
            hamming_decode(dst);
            printf("%s\n", dst);
        }
        else printf("Hamming code is INVALID. Error code: %d!\n", error_code);
    }
    else fprintf(stderr, "Error: output buffer is small.\n");
    return 0;
}