NetBSD/lib/libc/stdlib/radixsort.3

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.\" $NetBSD: radixsort.3,v 1.11 2002/02/07 07:00:30 ross Exp $
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.\"
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.\" Copyright (c) 1990, 1991, 1993
.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" from: @(#)radixsort.3 8.2 (Berkeley) 1/27/94
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.\"
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.Dd January 27, 1994
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.Dt RADIXSORT 3
.Os
.Sh NAME
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.Nm radixsort ,
.Nm sradixsort
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.Nd radix sort
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.Sh LIBRARY
.Lb libc
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.Sh SYNOPSIS
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.Fd #include \*[Lt]limits.h\*[Gt]
.Fd #include \*[Lt]stdlib.h\*[Gt]
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.Ft int
.Fn radixsort "const u_char **base" "int nmemb" "u_char *table" "u_int endbyte"
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.Ft int
.Fn sradixsort "const u_char **base" "int nmemb" "u_char *table" "u_int endbyte"
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.Sh DESCRIPTION
The
.Fn radixsort
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and
.Fn sradixsort
functions
are implementations of radix sort.
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.Pp
These functions sort an
.Fa nmemb
element array of pointers to byte strings, with
the initial member of which is referenced by
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.Fa base .
The byte strings may contain any values.
End of strings is denoted
by character which has same weight as user specified value
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.Fa endbyte .
.Fa endbyte
has to be between 0 and 255.
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.Pp
Applications may specify a sort order by providing the
.Fa table
argument.
If
.Pf non- Dv NULL ,
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.Fa table
must reference an array of
.Dv UCHAR_MAX
+ 1 bytes which contains the sort
weight of each possible byte value.
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The end-of-string byte must have a sort weight of 0 or 255
(for sorting in reverse order).
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More than one byte may have the same sort weight.
The
.Fa table
argument
is useful for applications which wish to sort different characters
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equally, for example, providing a table with the same weights
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for A-Z as for a-z will result in a case-insensitive sort.
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If
.Fa table
is NULL, the contents of the array are sorted in ascending order
according to the
.Tn ASCII
order of the byte strings they reference and
.Fa endbyte
has a sorting weight of 0.
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.Pp
The
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.Fn sradixsort
function is stable, that is, if two elements compare as equal, their
order in the sorted array is unchanged.
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The
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.Fn sradixsort
function uses additional memory sufficient to hold
.Fa nmemb
pointers.
.Pp
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The
.Fn radixsort
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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.
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.Sh RETURN VALUES
Upon successful completion 0 is returned.
Otherwise, \-1 is returned and the global variable
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.Va errno
is set to indicate the error.
.Sh ERRORS
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.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
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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
.Pp
.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
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.Rs
.%A McIlroy, P.
.%D 1993
.%B "Engineering Radix Sort"
.%T "Computing Systems"
.%V Vol. 6:1
.%P pp. 5-27
.Re
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.Sh HISTORY
The
.Fn radixsort
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function first appeared in
.Bx 4.4 .