NAME

radixsort, sradixsort — radix sort

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <limits.h>
#include <stdlib.h>

int
radixsort(const u_char **base, int nmemb, u_char *table, u_int endbyte);

int
sradixsort(const u_char **base, int nmemb, u_char *table, u_int endbyte);

DESCRIPTION

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

These functions sort an nmemb element array of pointers to byte strings, with the initial member of which is referenced by base. The byte strings may contain any values. End of strings is denoted by character which has same weight as user specified value endbyte. endbyte has to be between 0 and 255.

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., Sorting and Searching, The Art of Computer Programming, Vol. 3, pp. 170-178, 1968.

Paige, R., Three Partition Refinement Algorithms, SIAM J. Comput., No. 6, Vol. 16, 1987.

McIlroy, P., Computing Systems, Engineering Radix Sort, Vol. 6:1, pp. 5-27, 1993.

HISTORY

The radixsort() function first appeared in 4.4BSD.