RADIXSORT(3) | Library Functions Manual | RADIXSORT(3)

# 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

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 4.3BSD-Net/2.

August 4, 2022 | Debian