Issue #287: made CSR/CSC readers more robust against invalid input (case #1).
static double sec(struct timeval start, struct timeval end) {
  return ((double)(((end.tv_sec * 1000000 + end.tv_usec) - (start.tv_sec * 1000000 + start.tv_usec)))) / 1.0e6;
}

static double sec(struct timeval start, struct timeval end) {
  return ((double)(((end.tv_sec * 1000000 + end.tv_usec) - (start.tv_sec * 1000000 + start.tv_usec)))) / 1.0e6;
}
