lib/libc/stdlib/radixsort.3 - master - nerfur/openbsd-src

lib/libc/stdlib/radixsort.3
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jsg
change some 4.4BSD references to earlier releases
04 авг 2022, 09:20
04 авг 2022, 09:206e23b9d
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.\"	$OpenBSD: radixsort.3,v 1.14 2022/08/04 06:20:24 jsg Exp $
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.Dd $Mdocdate: August 4 2022 $
.Dt RADIXSORT 3
.Os
.Sh NAME
.Nm radixsort ,
.Nm sradixsort
.Nd radix sort
.Sh SYNOPSIS
.In limits.h
.In stdlib.h
.Ft int
.Fn radixsort "const u_char **base" "int nmemb" "const u_char *table" "u_int endbyte"
.Ft int
.Fn sradixsort "const u_char **base" "int nmemb" "const u_char *table" "u_int endbyte"
.Sh DESCRIPTION
The
.Fn radixsort
and
.Fn sradixsort
functions are implementations of radix sort.
.Pp
These functions sort an array of
.Fa nmemb
pointers to byte strings.
The initial member is referenced by
.Fa base .
The byte strings may contain any values; the end of each string
is denoted by the user-specified value
.Fa endbyte .
.Pp
Applications may specify a sort order by providing the
.Fa table
argument.
If non-null,
.Fa table
must reference an array of
.Dv 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
.Dv 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.
.Pp
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.
.Pp
The
.Fn radixsort
function is not stable, but uses no additional memory.
.Pp
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.
.Sh RETURN VALUES
.Rv -std
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er EINVAL
The value of the
.Fa endbyte
element of
.Fa table
is not 0 or 255.
.El
.Pp
Additionally, the
.Fn sradixsort
function may fail and set
.Va errno
for any of the errors specified for the library routine
.Xr malloc 3 .
.Sh SEE ALSO
.Xr sort 1 ,
.Xr qsort 3
.Rs
.%A Knuth, D.E.
.%D 1968
.%B "The Art of Computer Programming"
.%T "Sorting and Searching"
.%V Vol. 3
.%P pp. 170-178
.Re
.Rs
.%A Paige, R.
.%D 1987
.%T "Three Partition Refinement Algorithms"
.%J "SIAM J. Comput."
.%V Vol. 16
.%N No. 6
.Re
.Rs
.%A McIlroy, P.
.%D 1993
.%B "Engineering Radix Sort"
.%T "Computing Systems"
.%V Vol. 6:1
.%P pp. 5-27
.Re
.Sh HISTORY
The
.Fn radixsort
function first appeared in
.Bx 4.3 Net/2 .