BSD 4_4 release

[unix-history] / usr / src / lib / libc / stdlib / qsort.3

diff --git a/usr/src/lib/libc/stdlib/qsort.3 b/usr/src/lib/libc/stdlib/qsort.3
index 1f35ae8..4f449c7 100644 (file)
--- a/usr/src/lib/libc/stdlib/qsort.3
+++ b/usr/src/lib/libc/stdlib/qsort.3
@@ -1,66 +1,233 @@
-.\" Copyright (c) 1990 The Regents of the University of California.
-.\" All rights reserved.
+.\" Copyright (c) 1990, 1991, 1993
+.\"    The Regents of the University of California.  All rights reserved.

 .\"
 .\"

-.\" Redistribution and use in source and binary forms are permitted
-.\" provided that: (1) source distributions retain this entire copyright
-.\" notice and comment, and (2) distributions including binaries display
-.\" the following acknowledgement:  ``This product includes software
-.\" developed by the University of California, Berkeley and its contributors''
-.\" in the documentation or other materials provided with the distribution
-.\" and in all advertising materials mentioning features or use of this
-.\" software. Neither the name of the University nor the names of its
-.\" contributors may be used to endorse or promote products derived
-.\" from this software without specific prior written permission.
-.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
-.\" IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
-.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
+.\" This code is derived from software contributed to Berkeley by
+.\" the American National Standards Committee X3, on Information
+.\" Processing Systems.

 .\"
 .\"

-.\"    @(#)qsort.3     6.3 (Berkeley) 5/16/90
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 3. All advertising materials mentioning features or use of this software
+.\"    must display the following acknowledgement:
+.\"    This product includes software developed by the University of
+.\"    California, Berkeley and its contributors.
+.\" 4. Neither the name of the University nor the names of its contributors
+.\"    may be used to endorse or promote products derived from this software
+.\"    without specific prior written permission.

 .\"
 .\"

-.TH QSORT 3  "May 16, 1990"
-.UC 4
-.SH NAME
-qsort \- quicker sort
-.SH SYNOPSIS
-.nf
-.ft B
-#include <stdlib.h>
-
-void
-qsort(void *base, size_t nmemb, size_t size,
-int (*compar)(const void *, const void *));
-.ft R
-.fi
-.SH DESCRIPTION
-.I Qsort
-is an implementation of C.A.R. Hoare's ``quicksort'' algorithm.
-.PP
+.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\"     @(#)qsort.3    8.1 (Berkeley) 6/4/93
+.\"
+.Dd June 4, 1993
+.Dt QSORT 3
+.Os
+.Sh NAME
+.Nm qsort, heapsort, mergesort
+.Nd sort functions
+.Sh SYNOPSIS
+.Fd #include <stdlib.h>
+.Ft void
+.Fn qsort "void *base" "size_t nmemb" "size_t size" "int (*compar)(const void *, const void *)"
+.Ft int
+.Fn heapsort "void *base" "size_t nmemb" "size_t size" "int (*compar)(const void *, const void *)"
+.Ft int
+.Fn mergesort "void *base" "size_t nmemb" "size_t size" "int (*compar)(const void *, const void *)"
+.Sh DESCRIPTION
+The
+.Fn qsort
+function is a modified partition-exchange sort, or quicksort.

 The
 The

-.I qsort 
-function sorts an array of
-.I nmemb
+.Fn heapsort
+function is a modified selection sort.
+The
+.Fn mergesort
+function is a modified merge sort with exponential search
+intended for sorting data with pre-existing order.
+.Pp
+The
+.Fn qsort
+and
+.Fn heapsort
+functions sort an array of
+.Fa nmemb

 objects, the initial member of which is pointed to by
 objects, the initial member of which is pointed to by

-.IR base .
+.Fa base .

 The size of each object is specified by
 The size of each object is specified by

-.IR size .
-.PP
-The contents of the array are sorted in ascending order according to
+.Fa size .
+.Fn Mergesort
+behaves similarly, but
+.Em requires
+that
+.Fa size
+be greater than
+.Dq "sizeof(void *) / 2" .
+.Pp
+The contents of the array
+.Fa base
+are sorted in ascending order according to

 a comparison function pointed to by
 a comparison function pointed to by

-.IR compar ,
-which is called with two arguments that point to the objects being
+.Fa compar ,
+which requires two arguments pointing to the objects being

 compared.
 compared.

-.PP
+.Pp

 The comparison function must return an integer less than, equal to, or
 greater than zero if the first argument is considered to be respectively
 less than, equal to, or greater than the second.
 The comparison function must return an integer less than, equal to, or
 greater than zero if the first argument is considered to be respectively
 less than, equal to, or greater than the second.

-.PP
-If two members compare as equal, their order in the sorted array is
-undefined.
-.SH "SEE ALSO"
-sort(1)
-.SH STANDARDS
-.B Qsort
-conforms to ANSI X3.159-1989 (``ANSI C'').
-.SH BUGS
-The comparison routine may not itself call
-.IR qsort (3).
+.Pp
+The functions
+.Fn qsort
+and
+.Fn heapsort
+are
+.Em not
+stable, that is, if two members compare as equal, their order in
+the sorted array is undefined.
+The function
+.Fn mergesort
+is stable.
+.Pp
+The
+.Fn qsort
+function is an implementation of C.A.R. Hoare's ``quicksort'' algorithm,
+a variant of partition-exchange sorting; in particular, see D.E. Knuth's
+Algorithm Q.
+.Fn Qsort
+takes O N lg N average time.
+This implementation uses median selection to avoid its
+O N**2 worst-case behavior.
+.Pp
+The
+.Fn heapsort
+function is an implementation of J.W.J. William's ``heapsort'' algorithm,
+a variant of selection sorting; in particular, see D.E. Knuth's Algorithm H.
+.Fn Heapsort
+takes O N lg N worst-case time.
+Its
+.Em only
+advantage over
+.Fn qsort
+is that it uses almost no additional memory; while
+.Fn qsort
+does not allocate memory, it is implemented using recursion.
+.Pp
+The function
+.Fn mergesort
+requires additional memory of size
+.Fa nmemb *
+.Fa size 
+bytes; it should be used only when space is not at a premium.
+.Fn Mergesort
+is optimized for data with pre-existing order; its worst case
+time is O N lg N; its best case is O N.
+.Pp
+Normally,
+.Fn qsort
+is faster than
+.Fn mergesort
+is faster than
+.Fn heapsort .
+Memory availability and pre-existing order in the data can make this
+untrue.
+.Sh RETURN VALUES
+The
+.Fn qsort
+function
+returns no value.
+.Pp
+Upon successful completion,
+.Fn heapsort
+and
+.Fn mergesort
+return 0.
+Otherwise, they return \-1 and the global variable
+.Va errno
+is set to indicate the error.
+.Sh ERRORS
+The
+.Fn heapsort
+function succeeds unless:
+.Bl -tag -width Er
+.It Bq Er EINVAL
+The
+.Fa size
+argument is zero, or,
+the
+.Fa size
+argument to
+.Fn mergesort
+is less than
+.Dq "sizeof(void *) / 2" .
+.It Bq Er ENOMEM
+.Fn Heapsort
+or
+.Fn mergesort
+were unable to allocate memory.
+.El
+.Sh COMPATIBILITY
+Previous versions of
+.Fn qsort
+did not permit the comparison routine itself to call
+.Fn qsort 3 .
+This is no longer true.
+.Sh SEE ALSO
+.Xr sort 1 ,
+.Xr radixsort 3
+.Rs
+.%A Hoare, C.A.R.
+.%D 1962
+.%T "Quicksort"
+.%J "The Computer Journal"
+.%V 5:1
+.%P pp. 10-15
+.Re
+.Rs
+.%A Williams, J.W.J
+.%D 1964
+.%T "Heapsort"
+.%J "Communications of the ACM"
+.%V 7:1
+.%P pp. 347-348
+.Re
+.Rs
+.%A Knuth, D.E.
+.%D 1968
+.%B "The Art of Computer Programming"
+.%V Vol. 3
+.%T "Sorting and Searching"
+.%P pp. 114-123, 145-149
+.Re
+.Rs
+.%A Mcilroy, P.M.
+.%T "Optimistic Sorting and Information Theoretic Complexity"
+.%J "Fourth Annual ACM-SIAM Symposium on Discrete Algorithms"
+.%V January 1992
+.Re
+.Rs
+.%A Bentley, J.L.
+.%T "Engineering a Sort Function"
+.%J "bentley@research.att.com"
+.%V January 1992
+.Re
+.Sh STANDARDS
+The
+.Fn qsort
+function
+conforms to
+.St -ansiC .