# quicksort.awk --- Quicksort algorithm, with user-supplied
# comparison function
#
# Arnold Robbins, arnoldskeeve.com, Public Domain
# January 2009
# quicksort --- C.A.R. Hoare's quick sort algorithm. See Wikipedia
# or almost any algorithms or computer science text
#
# Adapted from K&R-II, page 110

function quicksort(data, left, right, less_than, i, last)
{
if (left >= right) # do nothing if array contains fewer
return # than two elements

quicksort_swap(data, left, int((left + right) / 2))
last = left
for (i = left + 1; i <= right; i++)
if (@less_than(data[i], data[left]))
quicksort_swap(data, ++last, i)
quicksort_swap(data, left, last)
quicksort(data, left, last - 1, less_than)
quicksort(data, last + 1, right, less_than)
}

# quicksort_swap --- helper function for quicksort, should really be inline

function quicksort_swap(data, i, j, temp)
{
temp = data[i]
data[i] = data[j]
data[j] = temp
}