HISTOGRAM_SIZE size of histograms: 256 + 1 to indicate that the string is finished.

INSERTION_SORT_THRESHOLD Below this size threshold, the sub-range is sorted using Insertion sort.

LENGTH_THRESHOLD buckets below this size will be sorted with introsort.

LEVEL_THRESHOLD after that many levels of recursion we fall back to introsort anyway this is used as a protection against the fact that radix sort performs worse when there are long common prefixes (probably because of cache locality).

SINGLE_MEDIAN_THRESHOLD Below this size threshold, the partition selection is simplified to a single median.