NAME
radixsort,
sradixsort —
radix sort
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#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
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
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
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.