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juce_TextDiff.cpp
1/*
2 ==============================================================================
3
4 This file is part of the JUCE library.
5 Copyright (c) 2017 - ROLI Ltd.
6
7 JUCE is an open source library subject to commercial or open-source
8 licensing.
9
10 The code included in this file is provided under the terms of the ISC license
11 http://www.isc.org/downloads/software-support-policy/isc-license. Permission
12 To use, copy, modify, and/or distribute this software for any purpose with or
13 without fee is hereby granted provided that the above copyright notice and
14 this permission notice appear in all copies.
15
16 JUCE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL WARRANTIES, WHETHER
17 EXPRESSED OR IMPLIED, INCLUDING MERCHANTABILITY AND FITNESS FOR PURPOSE, ARE
18 DISCLAIMED.
19
20 ==============================================================================
21*/
22
23 namespace juce
24{
25
26 struct TextDiffHelpers
27{
28 enum { minLengthToMatch = 3,
29 maxComplexity = 16 * 1024 * 1024 };
30
31 struct StringRegion
32 {
33 StringRegion (const String& s) noexcept
34 : text (s.getCharPointer()), start (0), length (s.length()) {}
35
36 StringRegion (String::CharPointerType t, int s, int len) noexcept
37 : text (t), start (s), length (len) {}
38
39 void incrementStart() noexcept { ++text; ++start; --length; }
40
41 String::CharPointerType text;
42 int start, length;
43 };
44
45 static void addInsertion (TextDiff& td, String::CharPointerType text, int index, int length)
46 {
47 TextDiff::Change c;
48 c.insertedText = String (text, (size_t) length);
49 c.start = index;
50 c.length = 0;
51 td.changes.add (c);
52 }
53
54 static void addDeletion (TextDiff& td, int index, int length)
55 {
56 TextDiff::Change c;
57 c.start = index;
58 c.length = length;
59 td.changes.add (c);
60 }
61
62 static void diffSkippingCommonStart (TextDiff& td, StringRegion a, StringRegion b)
63 {
64 for (;;)
65 {
66 auto ca = *a.text;
67 auto cb = *b.text;
68
69 if (ca != cb || ca == 0)
70 break;
71
72 a.incrementStart();
73 b.incrementStart();
74 }
75
76 diffRecursively (td, a, b);
77 }
78
79 static void diffRecursively (TextDiff& td, StringRegion a, StringRegion b)
80 {
81 int indexA = 0, indexB = 0;
82 auto len = findLongestCommonSubstring (a.text, a.length, indexA,
83 b.text, b.length, indexB);
84
85 if (len >= minLengthToMatch)
86 {
87 if (indexA > 0 && indexB > 0)
88 diffSkippingCommonStart (td, StringRegion (a.text, a.start, indexA),
89 StringRegion (b.text, b.start, indexB));
90 else if (indexA > 0)
91 addDeletion (td, b.start, indexA);
92 else if (indexB > 0)
93 addInsertion (td, b.text, b.start, indexB);
94
95 diffRecursively (td, StringRegion (a.text + (indexA + len), a.start + indexA + len, a.length - indexA - len),
96 StringRegion (b.text + (indexB + len), b.start + indexB + len, b.length - indexB - len));
97 }
98 else
99 {
100 if (a.length > 0) addDeletion (td, b.start, a.length);
101 if (b.length > 0) addInsertion (td, b.text, b.start, b.length);
102 }
103 }
104
105 static int findLongestCommonSubstring (String::CharPointerType a, const int lenA, int& indexInA,
106 String::CharPointerType b, const int lenB, int& indexInB) noexcept
107 {
108 if (lenA == 0 || lenB == 0)
109 return 0;
110
111 if (lenA * lenB > maxComplexity)
112 return findCommonSuffix (a, lenA, indexInA,
113 b, lenB, indexInB);
114
115 auto scratchSpace = sizeof (int) * (2 + 2 * (size_t) lenB);
116
117 if (scratchSpace < 4096)
118 {
119 auto* scratch = (int*) alloca (scratchSpace);
120 return findLongestCommonSubstring (a, lenA, indexInA, b, lenB, indexInB, scratchSpace, scratch);
121 }
122
123 HeapBlock<int> scratch (scratchSpace);
124 return findLongestCommonSubstring (a, lenA, indexInA, b, lenB, indexInB, scratchSpace, scratch);
125 }
126
127 static int findLongestCommonSubstring (String::CharPointerType a, const int lenA, int& indexInA,
128 String::CharPointerType b, const int lenB, int& indexInB,
129 const size_t scratchSpace, int* const lines) noexcept
130 {
131 zeromem (lines, scratchSpace);
132
133 auto* l0 = lines;
134 auto* l1 = l0 + lenB + 1;
135
136 int loopsWithoutImprovement = 0;
137 int bestLength = 0;
138
139 for (int i = 0; i < lenA; ++i)
140 {
141 auto ca = a.getAndAdvance();
142 auto b2 = b;
143
144 for (int j = 0; j < lenB; ++j)
145 {
146 if (ca != b2.getAndAdvance())
147 {
148 l1[j + 1] = 0;
149 }
150 else
151 {
152 auto len = l0[j] + 1;
153 l1[j + 1] = len;
154
155 if (len > bestLength)
156 {
157 loopsWithoutImprovement = 0;
158 bestLength = len;
159 indexInA = i;
160 indexInB = j;
161 }
162 }
163 }
164
165 if (++loopsWithoutImprovement > 100)
166 break;
167
168 std::swap (l0, l1);
169 }
170
171 indexInA -= bestLength - 1;
172 indexInB -= bestLength - 1;
173 return bestLength;
174 }
175
176 static int findCommonSuffix (String::CharPointerType a, int lenA, int& indexInA,
177 String::CharPointerType b, int lenB, int& indexInB) noexcept
178 {
179 int length = 0;
180 a += lenA - 1;
181 b += lenB - 1;
182
183 while (length < lenA && length < lenB && *a == *b)
184 {
185 --a;
186 --b;
187 ++length;
188 }
189
190 indexInA = lenA - length;
191 indexInB = lenB - length;
192 return length;
193 }
194};
195
196 TextDiff::TextDiff (const String& original, const String& target)
197{
198 TextDiffHelpers::diffSkippingCommonStart (*this, original, target);
199}
200
201 String TextDiff::appliedTo (String text) const
202{
203 for (auto& c : changes)
204 text = c.appliedTo (text);
205
206 return text;
207}
208
209 bool TextDiff::Change::isDeletion() const noexcept
210{
211 return insertedText.isEmpty();
212}
213
214 String TextDiff::Change::appliedTo (const String& text) const noexcept
215{
216 return text.replaceSection (start, length, insertedText);
217}
218
219
220//==============================================================================
221//==============================================================================
222#if JUCE_UNIT_TESTS
223
224 class DiffTests : public UnitTest
225{
226 public:
227 DiffTests()
228 : UnitTest ("TextDiff class", UnitTestCategories::text)
229 {}
230
231 static String createString (Random& r)
232 {
233 juce_wchar buffer[500] = { 0 };
234
235 for (int i = r.nextInt (numElementsInArray (buffer) - 1); --i >= 0;)
236 {
237 if (r.nextInt (10) == 0)
238 {
239 do
240 {
241 buffer[i] = (juce_wchar) (1 + r.nextInt (0x10ffff - 1));
242 }
243 while (! CharPointer_UTF16::canRepresent (buffer[i]));
244 }
245 else
246 buffer[i] = (juce_wchar) ('a' + r.nextInt (3));
247 }
248
249 return CharPointer_UTF32 (buffer);
250 }
251
252 void testDiff (const String& a, const String& b)
253 {
254 TextDiff diff (a, b);
255 auto result = diff.appliedTo (a);
256 expectEquals (result, b);
257 }
258
259 void runTest() override
260 {
261 beginTest ("TextDiff");
262
263 auto r = getRandom();
264
265 testDiff (String(), String());
266 testDiff ("x", String());
267 testDiff (String(), "x");
268 testDiff ("x", "x");
269 testDiff ("x", "y");
270 testDiff ("xxx", "x");
271 testDiff ("x", "xxx");
272
273 for (int i = 1000; --i >= 0;)
274 {
275 auto s = createString (r);
276 testDiff (s, createString (r));
277 testDiff (s + createString (r), s + createString (r));
278 }
279 }
280};
281
282 static DiffTests diffTests;
283
284#endif
285
286} // namespace juce
juce::Random
Definition: juce_Random.h:35
juce::Random::nextInt
int nextInt() noexcept
Definition: juce_Random.cpp:78
juce::String
Definition: juce_String.h:39
juce::String::isEmpty
bool isEmpty() const noexcept
Definition: juce_String.h:296
juce::String::replaceSection
String replaceSection(int startIndex, int numCharactersToReplace, StringRef stringToInsert) const
Definition: juce_String.cpp:1229
juce::TextDiff::TextDiff
TextDiff(const String &original, const String &target)
Definition: juce_TextDiff.cpp:196
juce::TextDiff::changes
Array< Change > changes
Definition: juce_TextDiff.h:71
juce::TextDiff::appliedTo
String appliedTo(String text) const
Definition: juce_TextDiff.cpp:201
juce::UnitTest
Definition: juce_UnitTest.h:70
juce::TextDiff::Change::appliedTo
String appliedTo(const String &original) const noexcept
Definition: juce_TextDiff.cpp:214
juce::TextDiff::Change::insertedText
String insertedText
Definition: juce_TextDiff.h:55
juce::TextDiff::Change::isDeletion
bool isDeletion() const noexcept
Definition: juce_TextDiff.cpp:209