RADIXSORT(3)

NAME
radixsort - radix sort

SYNOPSIS
#include <limits.h>
#include <stdlib.h>
int
radixsort(const unsigned char **base, int nmemb, const unsigned char *table, unsigned endbyte);
int
sradixsort(const unsigned char **base, int nmemb, const unsigned char *table, unsigned endbyte);

DESCRIPTION
The radixsort() and sradixsort() functions are implementations of radix sort.

These functions sort an array of pointers to byte strings, the initial member of which is referenced by base. The byte strings may contain any values; the end of each string is denoted by the user-specified value endbyte.

Applications may specify a sort order by providing the table argument. If non-NULL, table must reference an array of UCHAR_MAX + 1 bytes which contains the sort weight of each possible byte value. The end-of-string byte must have a sort weight of 0 or 255 (for sorting in reverse order). More than one byte may have the same sort weight. The table argument is useful for applications which wish to sort different characters equally, for example, providing a table with the same weights for A-Z as for a-z will result in a case-insensitive sort. If table is NULL, the contents of the array are sorted in ascending order according to the ASCII order of the byte strings they reference and endbyte has a sorting weight of 0.

The sradixsort() function is stable, that is, if two elements compare as equal, their order in the sorted array is unchanged. The sradixsort() function uses additional memory sufficient to hold nmemb pointers.

The radixsort() function is not stable, but uses no additional memory.

These functions are variants of most-significant-byte radix sorting; in particular, see D.E. Knuth's Algorithm R and section 5.2.5, exercise 10. They take linear time relative to the number of bytes in the strings.

RETURN VALUES
Upon successful completion 0 is returned. Otherwise, -1 is returned and the global variable errno is set to indicate the error.

ERRORS

[EINVAL]
    The value of the endbyte element of table is not 0 or 255.

Additionally, the sradixsort() function may fail and set errno for any of the errors specified for the library routine malloc(3).

SEE ALSO
sort(1), qsort(3)

Knuth, D.E., 1968, The Art of Computer Programming, Sorting and Searching, Vol. 3, pp. 170-178. Paige, R., 1987, Three Partition Refinement Algorithms, SIAM J. Comput., Vol. 16, No. 6. McIlroy, P., 1993, Engineering Radix Sort, Computing Systems, Vol. 6:1, pp. 5-27.

HISTORY
The radixsort() function first appeared in 4.4BSD.