private int getHighIndex (double t) {
	if (this.nt == 0)
		return -1;
	if (t <= this.t [0])
		return 0;
	if (t > this.t [this.nt-1])
		return this.nt;
	/* Start binary search. */
	int left = 0, right = this.nt-1;
	while (left < right - 1) {
		int mid = (left + right) / 2;
		if (t > this.t [mid]) left = mid; else right = mid;
	}
	//Melder_assert (right == left + 1);
	return right;
    }