radixsort(3)

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 implementa

tions 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-speci

fied 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 re

verse order).
More than one byte may have the same sort weight. The table

argument is
useful for applications which wish to sort different charac

ters 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 ele

ments 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 addi

tional 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.

BSD January 27, 1994

BSD