Format size in C

gistfile1.c

char* size(char* buffer, unsigned int length, unsigned int num) {
  // floor(log(pow(2, 64)) / log(1024)) = 6
  const char* unit[] = {
    "B", "KB", "MB", "GB", "TB", "PB", "EB"
  };

  if (num == 0) {
    snprintf(buffer, length, "0 %s", unit[0]);
  } else {
    unsigned int base = floor(log(num) / log(1024));

    snprintf(buffer, length, "%.2f %s", num / pow(1024, base), unit[base]);
  }

  return buffer;
}