child++
		}
		if !(cmp(data[first+root], data[first+child]) < 0) {
			return
		}
		data[first+root], data[first+child] = data[first+child], data[first+root]
		root = child
	}
}

func heapSortCmpFunc[E any](data []E, a, b int, cmp func(a, b E) int) {
	first := a
	lo := 0
	hi := b - a

	// Build heap with greatest element at top.
	for i := (hi - 1) / 2; i >= 0; i-- {
		siftDownCmpFunc(data, i, hi, first, cmp)