Read raw mouse coordinates from Linux /dev/input/mouse*

#include <inttypes.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>

int main(int argc, char *argv[]) {
  char *input_dev = (argc > 1) ? argv[1] : "/dev/input/mouse0";
  int fd;
  uint8_t mouse_inp[3];
  int x = 0, y = 0;

  if ((fd = open(input_dev, O_RDONLY)) == -1) {
    perror("open");
    return -1;
  }
  while (read(fd, mouse_inp, sizeof(mouse_inp))) {
    if (mouse_inp[0] & 0x1) {
      x = 0;
      y = 0;
    }
    else {
      x += (int8_t)mouse_inp[1];
      y += (int8_t)mouse_inp[2];
    }
    printf("x = %+d\ty = %+d\n", x, y);
    fflush(stdout);
  }
  return 0;
}