NAME
radixsort,
sradixsort —
radix sort
SYNOPSIS
#include
<limits.h>
#include <stdlib.h>
int
radixsort(const
u_char **base, int
nmemb, const u_char
*table, u_int
endbyte);
int
sradixsort(const
u_char **base, int
nmemb, const u_char
*table, u_int
endbyte);
DESCRIPTION
The
radixsort()
and sradixsort() functions are implementations of
radix sort.
These functions sort an array of nmemb pointers to byte strings. The initial member 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, the value 0 is returned; 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
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.