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 28  .\"     @(#)radixsort.3	8.2 (Berkeley) 1/27/94
 29  .\" $FreeBSD: src/lib/libc/stdlib/radixsort.3,v 1.12 2007/01/09 00:28:10 imp Exp $
 30  .\"
 31  .Dd January 27, 1994
 32  .Dt RADIXSORT 3
 33  .Os
 34  .Sh NAME
 35  .Nm radixsort , sradixsort
 36  .Nd radix sort
 37  .Sh LIBRARY
 38  .Lb libc
 39  .Sh SYNOPSIS
 40  .In limits.h
 41  .In stdlib.h
 42  .Ft int
 43  .Fn radixsort "const unsigned char **base" "int nmemb" "const unsigned char *table" "unsigned endbyte"
 44  .Ft int
 45  .Fn sradixsort "const unsigned char **base" "int nmemb" "const unsigned char *table" "unsigned endbyte"
 46  .Sh DESCRIPTION
 47  The
 48  .Fn radixsort
 49  and
 50  .Fn sradixsort
 51  functions
 52  are implementations of radix sort.
 53  .Pp
 54  These functions sort an array of pointers to byte strings, the initial
 55  member of which is referenced by
 56  .Fa base .
 57  The byte strings may contain any values; the end of each string
 58  is denoted by the user-specified value
 59  .Fa endbyte .
 60  .Pp
 61  Applications may specify a sort order by providing the
 62  .Fa table
 63  argument.
 64  If
 65  .Pf non- Dv NULL ,
 66  .Fa table
 67  must reference an array of
 68  .Dv UCHAR_MAX
 69  + 1 bytes which contains the sort
 70  weight of each possible byte value.
 71  The end-of-string byte must have a sort weight of 0 or 255
 72  (for sorting in reverse order).
 73  More than one byte may have the same sort weight.
 74  The
 75  .Fa table
 76  argument
 77  is useful for applications which wish to sort different characters
 78  equally, for example, providing a table with the same weights
 79  for A-Z as for a-z will result in a case-insensitive sort.
 80  If
 81  .Fa table
 82  is NULL, the contents of the array are sorted in ascending order
 83  according to the
 84  .Tn ASCII
 85  order of the byte strings they reference and
 86  .Fa endbyte
 87  has a sorting weight of 0.
 88  .Pp
 89  The
 90  .Fn sradixsort
 91  function is stable, that is, if two elements compare as equal, their
 92  order in the sorted array is unchanged.
 93  The
 94  .Fn sradixsort
 95  function uses additional memory sufficient to hold
 96  .Fa nmemb
 97  pointers.
 98  .Pp
 99  The
100  .Fn radixsort
101  function is not stable, but uses no additional memory.
102  .Pp
103  These functions are variants of most-significant-byte radix sorting; in
104  particular, see
105  .An "D.E. Knuth" Ns 's
106  .%T "Algorithm R"
107  and section 5.2.5, exercise 10.
108  They take linear time relative to the number of bytes in the strings.
109  .Sh RETURN VALUES
110  .Rv -std radixsort
111  .Sh ERRORS
112  .Bl -tag -width Er
113  .It Bq Er EINVAL
114  The value of the
115  .Fa endbyte
116  element of
117  .Fa table
118  is not 0 or 255.
119  .El
120  .Pp
121  Additionally, the
122  .Fn sradixsort
123  function
124  may fail and set
125  .Va errno
126  for any of the errors specified for the library routine
127  .Xr malloc 3 .
128  .Sh SEE ALSO
129  .Xr sort 1 ,
130  .Xr qsort 3
131  .Pp
132  .Rs
133  .%A Knuth, D.E.
134  .%D 1968
135  .%B "The Art of Computer Programming"
136  .%T "Sorting and Searching"
137  .%V Vol. 3
138  .%P pp. 170-178
139  .Re
140  .Rs
141  .%A Paige, R.
142  .%D 1987
143  .%T "Three Partition Refinement Algorithms"
144  .%J "SIAM J. Comput."
145  .%V Vol. 16
146  .%N No. 6
147  .Re
148  .Rs
149  .%A McIlroy, P.
150  .%D 1993
151  .%B "Engineering Radix Sort"
152  .%T "Computing Systems"
153  .%V Vol. 6:1
154  .%P pp. 5-27
155  .Re
156  .Sh HISTORY
157  The
158  .Fn radixsort
159  function first appeared in
160  .Bx 4.4 .