NAME

     radixsort, sradixsort — radix sort

LIBRARY

     Utility functions from BSD systems (libbsd, -lbsd)

SYNOPSIS

     #include <limits.h>
     #include <stdlib.h>
     (See libbsd(7) for include usage.)

     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 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

     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

     [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.