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BinarySearch.h
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1//# BinarySearch.h: Binary search through linear, sorted, data structures
2//# Copyright (C) 1995,1996,1999
3//# Associated Universities, Inc. Washington DC, USA.
4//#
5//# This library is free software; you can redistribute it and/or modify it
6//# under the terms of the GNU Library General Public License as published by
7//# the Free Software Foundation; either version 2 of the License, or (at your
8//# option) any later version.
9//#
10//# This library is distributed in the hope that it will be useful, but WITHOUT
11//# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12//# FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public
13//# License for more details.
14//#
15//# You should have received a copy of the GNU Library General Public License
16//# along with this library; if not, write to the Free Software Foundation,
17//# Inc., 675 Massachusetts Ave, Cambridge, MA 02139, USA.
18//#
19//# Correspondence concerning AIPS++ should be addressed as follows:
20//# Internet email: aips2-request@nrao.edu.
21//# Postal address: AIPS++ Project Office
22//# National Radio Astronomy Observatory
23//# 520 Edgemont Road
24//# Charlottesville, VA 22903-2475 USA
25//#
26//#
27//# $Id$
28
29
30#ifndef CASA_BINARYSEARCH_H
31#define CASA_BINARYSEARCH_H
32
33//# Includes
34#include <casacore/casa/aips.h>
35
36namespace casacore { //# NAMESPACE CASACORE - BEGIN
37
38// <summary>
39// Binary search a sorted, linear, data structure.
40// </summary>
41
42// <reviewed reviewer="Ger van Diepen" date="1995/03/31" tests="tBinarySearch" demos="">
43// </reviewed>
44
45// <synopsis>
46// These binary search functions work on sorted, linear data structures
47// which have operator() or operator[] defined on them (<i>e.g.</i>
48// C-array, Vector, IPosition, Block, ScalarColumn, <i>etc.</i>)
49// Two versions of the functions are provided, one which uses
50// parentheses () for indexing, one which uses square brackets [] (obviously
51// the latter one can also be used for ordinary C-style pointers and arrays).
52// It is assumed that the container uses zero-based indexing.
53//
54// The container must be sorted (sorting is available through the
55// <linkto class="Sort">Sort</linkto> and
56// <linkto class="GenSort">GenSort</linkto>
57// classes, and from various
58// <linkto class="Table">Table</linkto> sort functions). The returned index
59// is in the range [0..n] inclusive. That is, from the first element of the
60// container to one past the last element of the container (zero-based indices).
61// If the container is sorted in ascending order, the returned index is the
62// first one whose element is greater than or equal to the searched for value.
63// If it is sorted in descending order, the returned index is the first which
64// is less than or equal to the searched for value. That is, the returned
65// index gives the position at which the value would be inserted (possibly
66// either at the end, or requiring the existing values to be "pushed" to the
67// right) maintaining the sort order. Obviously index n can only be
68// returned if the value searched for is past the end of the array, thus
69// has to be inserted at the end.
70//
71// The functions determine for themselves whether the container is sorted in
72// ascending or descending order by comparing the first and last element.
73// <note role=tip>
74// While normally you want to search a container with indices in the range
75// <src>[0 ... n-1]</src>, any desired lower bound may be used instead.
76// </note>
77// <note role=warning>
78// The functions do not check if the container is valid, <i>i.e.</i> if
79// the container is sorted and if the container does not contain duplicate
80// values.
81// </note>
82//
83// These functions loosely follow some written by Ger van Diepen in a more
84// specialized context.
85// </synopsis>
86//
87// <example>
88// <srcblock>
89// Vector<Int> vi;
90// ... // Sets vi somehow
91// genSort(vi);
92// Int val;
93// Bool found;
94// while (cin >> val && val != -999) {
95// Int where = binarySearch(found, vi, val, vi.nelements());
96// if (found) {
97// cout << "Found " << val << " at position " << where << endl;
98// } else {
99// cout << val << " is not in the vector, but it belongs at " <<
100// where << endl;
101// }
102// }
103// </srcblock>
104// </example>
105//
106// <motivation>
107// I found that I (BEG) was writing binary search functions several times,
108// for example when checking whether the cached off and gain scans in time
109// sorted data needed to be refilled. It generally seems like a useful little
110// utility function.
111// </motivation>
112//
113// <templating arg=Container>
114// <li> operator(Int) or operator[Int] needs to be defined.
115// <li> The index must be zero based.
116// <li> The result of that indexing must be an expression that can be
117// compared with an object of class ElType. Normally in fact it would
118// be a temporary of class ElType.
119// </templating>
120// <templating arg=ElType>
121// <li> The less than operator (<) and greater than (>) operators need to
122// be defined, and have their usual ordering relations.
123// </templating>
124//
125// <todo asof="yyyy/mm/dd">
126// <li> I suspect that an implementation is possible that only calls
127// operator() or [] once during each evaluation of the while loop.
128// <li> MACROize implementation so that code isn't repeated twice. Or,
129// possibly implement one using the other (e.g. by introducing an adapter
130// class that turns (i) into [i].
131// </todo>
132
133
134// <group name=binarysearch>
136// Search <i>container</i> for <i>value</i>. There are assumed to be at least
137// <i>n</i> elements in the container. The container will be searched for
138// indices in the range <src>[lower ... lower + n - 1]</src> Return the index
139// of the first element which is greater than or equal to (ascending order) or
140// less than or equal to (descending order) the value.
141// <group>
142// This version of the function is for containers that use () for indexing.
143template<class Container, class ElType>
144 Int binarySearch(Bool &found, const Container &container,
145 const ElType &value, uInt n, Int lower=0);
146// This version of the function is for containers that use [] for indexing.
147template<class Container, class ElType>
148 Int binarySearchBrackets(Bool &found, const Container &container,
149 const ElType &value, uInt n, Int lower=0);
150// </group>
151// </group>
152
153
154} //# NAMESPACE CASACORE - END
155
156#ifndef CASACORE_NO_AUTO_TEMPLATES
157#include <casacore/casa/Utilities/BinarySearch.tcc>
158#endif //# CASACORE_NO_AUTO_TEMPLATES
159#endif
this file contains all the compiler specific defines
Definition mainpage.dox:28
unsigned int uInt
Definition aipstype.h:51
int Int
Definition aipstype.h:50
bool Bool
Define the standard types used by Casacore.
Definition aipstype.h:42
LatticeExprNode value(const LatticeExprNode &expr)
This function returns the value of the expression without a mask.
Int binarySearch(Bool &found, const Container &container, const ElType &value, uInt n, Int lower=0)
Search container for value.
Int binarySearchBrackets(Bool &found, const Container &container, const ElType &value, uInt n, Int lower=0)
This version of the function is for containers that use [] for indexing.