hexdump -C compatible output; useful for debugging

hexdump.c

#include <stdio.h>
#include <string.h>
#include <inttypes.h>

#define HEXDUMP_MIN(X, Y) ((X) < (Y) ? (X) : (Y))

static void hexdump8(FILE *out, const uint8_t *first, const uint8_t *last) {
  const uint8_t *stop = HEXDUMP_MIN(first + 8, last);
  const uint8_t *k;
  for(k = first; k != stop; ++k) {
    fprintf(out, "%02x ", *k);
  }
  // each byte needs 3 spaces (2 hex value and space)
  for(; stop != first + 8; ++stop) {
    fputs("   ", out);
  }
  // we have extra space after 8 bytes
  fputc(' ', out);
}

static void hexdump(FILE *out, const uint8_t *src, size_t len) {
  size_t buflen = 0;
  int repeated = 0;
  uint8_t buf[16];
  const uint8_t *end, *i;
  if(len == 0) {
    return;
  }
  end = src + len;
  i = src;
  for(;;) {
    const uint8_t *stop;
    uint8_t *p;
    size_t nextlen = HEXDUMP_MIN(16, end - i);
    if(nextlen == buflen && memcmp(buf, i, buflen) == 0) {
      // as long as adjacent 16 bytes block are the same, we just
      // print single '*'.
      if(!repeated) {
        repeated = 1;
        fputs("*\n", out);
      }
      i += nextlen;
      continue;
    }
    repeated = 0;
    fprintf(out, "%08lx", i - src);
    if(i == end) {
      fputc('\n', out);
      break;
    }
    fputs("  ", out);
    hexdump8(out, i, end);
    hexdump8(out, i + 8, i + 8 < end ? end : i + 8);
    fputc('|', out);
    stop = HEXDUMP_MIN(i + 16, end);
    buflen = stop - i;
    p = buf;
    for(; i != stop; ++i) {
      *p++ = *i;
      if(0x20 <= *i && *i <= 0x7e) {
        fputc(*i, out);
      }
      else {
        fputc('.', out);
      }
    }
    fputs("|\n", out);
  }
}

int main() {
  const uint8_t b[] = "hello\x00world\r\n";
  hexdump(stderr, b, sizeof(b));
}