NAME    [Toc]    [Back]

     radixsort -- radix sort

LIBRARY    [Toc]    [Back]

     Standard C Library (libc, -lc)

SYNOPSIS    [Toc]    [Back]

     #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    [Toc]    [Back]

     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    [Toc]    [Back]

     The radixsort() function returns the value 0 if successful; otherwise the
     value -1 is returned and the global variable errno is set to indicate the
     error.

ERRORS    [Toc]    [Back]

     [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    [Toc]    [Back]

     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    [Toc]    [Back]

     The radixsort() function first appeared in 4.4BSD.


FreeBSD 5.2.1		       January 27, 1994 		 FreeBSD 5.2.1