Binary search implementation that returns insertion index if element not found

RandomAccessCollection+BinarySearch.swift

import Foundation

public extension RandomAccessCollection {
    func binarySearch(startIndex: Index? = nil, endIndex: Index? = nil, comparator: (Element) -> Int) -> (index: Index, found: Bool) {
        var low = startIndex ?? self.startIndex
        var high = index(before: endIndex ?? self.endIndex)

        while low <= high {
            let mid = index(low, offsetBy: distance(from: low, to: high) >> 1)
            let midVal = self[mid]

            let cmp = comparator(midVal)

            if cmp < 0 {
                low = index(after: mid)
            } else if cmp > 0 {
                high = index(before: mid)
            } else {
                return (index: mid, found: true)
            }
        }

        return (index: low, found: false)
    }
}