NAME
radixsort,
sradixsort —
radix sort
LIBRARY
library “libc”
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
Theradixsort()
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
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.