inspired by hexcmp, bitcmp is a tool to view `cmp -l` output in bitwise form

bitcmp.c

#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

/*
 * Print the bits in the 2nd file that are different from the 1st file
 *
 * E.g.,
 * cmp -l <(dd if=/dev/urandom count=1) \
 *        <(dd if=/dev/urandom count=1) \
 *        | bitcmp -o
 */

int main(int argc, char *argv[]) {
  int value_base = 10;
  int offset_base = 10;
  bool inverse = false;

  for (int opt; (opt = getopt(argc, argv, "oOxXv")) != -1;) {
    switch (opt) {
    case 'o':
      value_base = 8;
      break;
    case 'O':
      offset_base = 8;
      break;
    case 'x':
      value_base = 16;
      break;
    case 'X':
      offset_base = 16;
      break;
    case 'v':
      inverse = true;
      break;
    default:
      fprintf(stderr, "usage: %s [OPTION]...\n", argv[0]);
      exit(EXIT_FAILURE);
    }
  }

  for (char buf[256]; fgets(buf, sizeof(buf), stdin);) {
    char bytenumstr[16], leftstr[16], rightstr[16];
    if (sscanf(buf, "%s %s %s", bytenumstr, leftstr, rightstr) != 3) {
      fprintf(stderr, "unexpected input: %s\n", buf);
      continue;
    }

    // convert byte number to offset
    int offset = strtol(bytenumstr, NULL, offset_base) - 1;
    int left = strtol(leftstr, NULL, value_base);
    int right = strtol(rightstr, NULL, value_base);

    if (inverse) {
      int tmp = right;
      right = left;
      left = tmp;
    }

    if (left < 0 || left > 0xFF || right < 0 || right > 0xFF) {
      fprintf(stderr, "unexpected input: %s\n", buf);
      continue;
    }

    int diff = left ^ right;

    char diffbit[9] = {'.', '.', '.', '.', '.', '.', '.', '.', '\0'};
    char outbit[9] = {'.', '.', '.', '.', '.', '.', '.', '.', '\0'};

    for (int i = 0; i < 8; i++) {
      if ((diff >> i) & 1) {
        diffbit[7 - i] = (left >> i) & 1 ? '0' : '1';
        outbit[7 - i] = diffbit[7 - i];
      } else {
        if ((left >> i) & 1) {
          outbit[7 - i] = '1';
        }
      }
    }

    printf("0x%08X %s %s\n", offset, diffbit, outbit);
  }

  exit(EXIT_SUCCESS);
}