RADIXSORT

 

NAME

radixsort sradixsort – radix sort  

LIBRARY

Lb libbsd  

SYNOPSIS

In limits.h In bsd/stdlib.h Ft int Fn radixsort const unsigned char **base int nmemb const unsigned char *table unsigned endbyte Ft int Fn sradixsort const unsigned char **base int nmemb const unsigned char *table unsigned endbyte  

DESCRIPTION

The Fn radixsort and Fn sradixsort functions are implementations of radix sort.

These functions sort an Fa nmemb element array of pointers to byte strings, with the initial member of which is referenced by Fa base . The byte strings may contain any values. End of strings is denoted by character which has same weight as user specified value Fa endbyte . Fa endbyte has to be between 0 and 255.

Applications may specify a sort order by providing the Fa table argument. If non- NULL Fa 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 Fa 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 Fa 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 Fa endbyte has a sorting weight of 0.

The Fn sradixsort function is stable, that is, if two elements compare as equal, their order in the sorted array is unchanged. The Fn sradixsort function uses additional memory sufficient to hold Fa nmemb pointers.

The Fn radixsort function is not stable, but uses no additional memory.

These functions are variants of most-significant-byte radix sorting; in particular, see An D.E. Knuth Ns ‘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

Rv -std radixsort  

ERRORS

Bq Er EINVAL

The value of the Fa endbyte element of Fa table is not 0 or 255.

Additionally, the Fn sradixsort function may fail and set errno for any of the errors specified for the library routine malloc(3).

Knuth, D.E. 1968 "The Art of Computer Programming" "Sorting and Searching" Vol. 3 pp. 170-178

Paige, R. 1987 "Three Partition Refinement Algorithms" "SIAM J. Comput." Vol. 16 No. 6

McIlroy, P. 1993 "Engineering Radix Sort" "Computing Systems" Vol. 6:1 pp. 5-27

 

HISTORY

The Fn radixsort function first appeared in BSD 4.4