package numerics

// Bisect returns the largest index i in [imin, imax] such that f(i) < target,
// assuming f is monotonically nondecreasing on that range.
//
// If target <= f(imin), returns imin. If target > f(imax), returns imax.
// Performs O(log(imax-imin)) evaluations of f.
func Bisect(imin, imax int, target float64, f func(i int) float64) int {
	lo, hi := imin, imax
	for lo < hi {
		mid := (lo + hi + 1) / 2
		if target <= f(mid) {
			hi = mid - 1
		} else {
			lo = mid
		}
	}
	return lo
}