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Diff.h
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/*
* Copyright 2008 Google Inc. All Rights Reserved.
* Author: fraser@google.com (Neil Fraser)
* Author: mikeslemmer@gmail.com (Mike Slemmer)
* Author: snhere@gmail.com (Sergey Nozhenko)
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* Diff Match and Patch
* http://code.google.com/p/google-diff-match-patch/
*/
#ifndef DIFF_MATCH_PATCH_H
#define DIFF_MATCH_PATCH_H
#include <limits>
#include <list>
#include <map>
#include <string>
#include <vector>
#include <algorithm>
#include <cstdlib>
#include <cwchar>
#include <time.h>
#include "llvm/Support/ErrorHandling.h"
/*
* Functions for diff, match and patch.
* Computes the difference between two texts to create a patch.
* Applies the patch onto another text, allowing for errors.
*
* @author fraser@google.com (Neil Fraser)
*
* Qt/C++ port by mikeslemmer@gmail.com (Mike Slemmer)
*
* STL-only port by snhere@gmail.com (Sergey Nozhenko)
* and some tweaks for std::string by leutloff@sundancer.oche.de (Christian Leutloff)
*
* Here is a trivial sample program:
*
#include "diff_match_patch.h"
#include <string>
using namespace std;
int main(int argc, char **argv) {
diff_match_patch<wstring> dmp;
wstring str1 = L"First string in diff";
wstring str2 = L"Second string in diff";
wstring strPatch = dmp.patch_toText(dmp.patch_make(str1, str2));
pair<wstring, vector<bool> > out
= dmp.patch_apply(dmp.patch_fromText(strPatch), str1);
wstring strResult = out.first;
// here, strResult will equal str2 above.
return 0;
}
*/
// Character type dependencies
template <class char_t> struct diff_match_patch_traits {};
/**
* Class containing the diff, match and patch methods.
* Also contains the behaviour settings.
*/
template <class stringT, class traits = diff_match_patch_traits<typename stringT::value_type> >
class diff_match_patch {
public:
/**
* String and character types
*/
typedef stringT string_t;
typedef typename string_t::value_type char_t;
/**-
* The data structure representing a diff is a Linked list of Diff objects:
* {Diff(Operation.DELETE, "Hello"), Diff(Operation.INSERT, "Goodbye"),
* Diff(Operation.EQUAL, " world.")}
* which means: delete "Hello", add "Goodbye" and keep " world."
*/
enum Operation {
DELETE, INSERT, EQUAL
};
/**
* Class representing one diff operation.
*/
class Diff {
public:
Operation operation;
// One of: INSERT, DELETE or EQUAL.
string_t text;
// The text associated with this diff operation.
/**
* Constructor. Initializes the diff with the provided values.
* @param _operation One of INSERT, DELETE or EQUAL.
* @param _text The text being applied.
*/
Diff(Operation _operation, const string_t &_text) : operation(_operation), text(_text) {}
Diff() {}
/**
* Display a human-readable version of this Diff.
* @return text version.
*/
string_t toString() const {
string_t prettyText = text;
// Replace linebreaks with Pilcrow signs.
for (typename string_t::iterator i = prettyText.begin(); i != prettyText.end(); ++i)
if (traits::to_wchar(*i) == L'\n') *i = traits::from_wchar(L'\u00b6');
return traits::cs(L"Diff(") + strOperation(operation) + traits::cs(L",\"") + prettyText + traits::cs(L"\")");
}
/**
* Is this Diff equivalent to another Diff?
* @param d Another Diff to compare against
* @return true or false
*/
bool operator==(const Diff &d) const {
return (d.operation == this->operation) && (d.text == this->text);
}
bool operator!=(const Diff &d) const { return !(operator == (d)); }
static string_t strOperation(Operation op) {
switch (op) {
case INSERT:
return traits::cs(L"INSERT");
case DELETE:
return traits::cs(L"DELETE");
case EQUAL:
return traits::cs(L"EQUAL");
}
llvm_unreachable("Invalid operation.");
}
};
typedef std::list<Diff> Diffs;
/**
* Class representing one patch operation.
*/
class Patch {
public:
Diffs diffs;
int start1;
int start2;
int length1;
int length2;
/**
* Constructor. Initializes with an empty list of diffs.
*/
Patch() : start1(0), start2(0), length1(0), length2(0) {}
bool isNull() const {
return start1 == 0 && start2 == 0 && length1 == 0 && length2 == 0 && diffs.empty();
}
/**
* Emulate GNU diff's format.
* Header: @@ -382,8 +481,9 @@
* Indices are printed as 1-based, not 0-based.
* @return The GNU diff string
*/
string_t toString() const {
string_t coords1, coords2;
if (length1 == 0) {
coords1 = to_string(start1) + traits::cs(L",0");
} else if (length1 == 1) {
coords1 = to_string(start1 + 1);
} else {
coords1 = to_string(start1 + 1) + traits::from_wchar(L',') + to_string(length1);
}
if (length2 == 0) {
coords2 = to_string(start2) + traits::cs(L",0");
} else if (length2 == 1) {
coords2 = to_string(start2 + 1);
} else {
coords2 = to_string(start2 + 1) + traits::from_wchar(L',') + to_string(length2);
}
string_t text(traits::cs(L"@@ -") + coords1 + traits::cs(L" +") + coords2 + traits::cs(L" @@\n"));
// Escape the body of the patch with %xx notation.
for (typename Diffs::const_iterator cur_diff = diffs.begin(); cur_diff != diffs.end(); ++cur_diff) {
switch ((*cur_diff).operation) {
case INSERT:
text += traits::from_wchar(L'+');
break;
case DELETE:
text += traits::from_wchar(L'-');
break;
case EQUAL:
text += traits::from_wchar(L' ');
break;
}
append_percent_encoded(text, (*cur_diff).text);
text += traits::from_wchar(L'\n');
}
return text;
}
};
typedef std::list<Patch> Patches;
friend class diff_match_patch_test;
public:
// Defaults.
// Set these on your diff_match_patch instance to override the defaults.
// Number of seconds to map a diff before giving up (0 for infinity).
float Diff_Timeout;
// Cost of an empty edit operation in terms of edit characters.
short Diff_EditCost;
// At what point is no match declared (0.0 = perfection, 1.0 = very loose).
float Match_Threshold;
// How far to search for a match (0 = exact location, 1000+ = broad match).
// A match this many characters away from the expected location will add
// 1.0 to the score (0.0 is a perfect match).
int Match_Distance;
// When deleting a large block of text (over ~64 characters), how close does
// the contents have to match the expected contents. (0.0 = perfection,
// 1.0 = very loose). Note that Match_Threshold controls how closely the
// end points of a delete need to match.
float Patch_DeleteThreshold;
// Chunk size for context length.
short Patch_Margin;
// The number of bits in an int.
short Match_MaxBits;
public:
diff_match_patch() :
Diff_Timeout(1.0f),
Diff_EditCost(4),
Match_Threshold(0.5f),
Match_Distance(1000),
Patch_DeleteThreshold(0.5f),
Patch_Margin(4),
Match_MaxBits(32) {
}
// DIFF FUNCTIONS
/**
* Find the differences between two texts.
* @param text1 Old string to be diffed.
* @param text2 New string to be diffed.
* @param checklines Speedup flag. If false, then don't run a
* line-level diff first to identify the changed areas.
* If true, then run a faster slightly less optimal diff.
* Most of the time checklines is wanted, so default to true.
* @return Linked List of Diff objects.
*/
Diffs diff_main(const string_t &text1, const string_t &text2, bool checklines = true) const {
// Set a deadline by which time the diff must be complete.
clock_t deadline;
if (Diff_Timeout <= 0) {
deadline = std::numeric_limits<clock_t>::max();
} else {
deadline = clock() + (clock_t)(Diff_Timeout * CLOCKS_PER_SEC);
}
Diffs diffs;
diff_main(text1, text2, checklines, deadline, diffs);
return diffs;
}
/**
* Find the differences between two texts. Simplifies the problem by
* stripping any common prefix or suffix off the texts before diffing.
* @param text1 Old string to be diffed.
* @param text2 New string to be diffed.
* @param checklines Speedup flag. If false, then don't run a
* line-level diff first to identify the changed areas.
* If true, then run a faster slightly less optimal diff.
* @param deadline Time when the diff should be complete by. Used
* internally for recursive calls. Users should set DiffTimeout instead.
* @param diffs Linked List of Diff objects.
*/
private:
static void diff_main(const string_t &text1, const string_t &text2, bool checklines, clock_t deadline, Diffs& diffs) {
diffs.clear();
// Check for equality (speedup).
if (text1 == text2) {
if (!text1.empty()) {
diffs.push_back(Diff(EQUAL, text1));
}
}
else {
// Trim off common prefix (speedup).
int commonlength = diff_commonPrefix(text1, text2);
const string_t &commonprefix = text1.substr(0, commonlength);
string_t textChopped1 = text1.substr(commonlength);
string_t textChopped2 = text2.substr(commonlength);
// Trim off common suffix (speedup).
commonlength = diff_commonSuffix(textChopped1, textChopped2);
const string_t &commonsuffix = right(textChopped1, commonlength);
textChopped1 = textChopped1.substr(0, textChopped1.length() - commonlength);
textChopped2 = textChopped2.substr(0, textChopped2.length() - commonlength);
// Compute the diff on the middle block.
diff_compute(textChopped1, textChopped2, checklines, deadline, diffs);
// Restore the prefix and suffix.
if (!commonprefix.empty()) {
diffs.push_front(Diff(EQUAL, commonprefix));
}
if (!commonsuffix.empty()) {
diffs.push_back(Diff(EQUAL, commonsuffix));
}
diff_cleanupMerge(diffs);
}
}
/**
* Find the differences between two texts. Assumes that the texts do not
* have any common prefix or suffix.
* @param text1 Old string to be diffed.
* @param text2 New string to be diffed.
* @param checklines Speedup flag. If false, then don't run a
* line-level diff first to identify the changed areas.
* If true, then run a faster slightly less optimal diff.
* @param deadline Time when the diff should be complete by.
* @param diffs Linked List of Diff objects.
*/
private:
static void diff_compute(string_t text1, string_t text2, bool checklines, clock_t deadline, Diffs& diffs) {
if (text1.empty()) {
// Just add some text (speedup).
diffs.push_back(Diff(INSERT, text2));
return;
}
if (text2.empty()) {
// Just delete some text (speedup).
diffs.push_back(Diff(DELETE, text1));
return;
}
{
const string_t& longtext = text1.length() > text2.length() ? text1 : text2;
const string_t& shorttext = text1.length() > text2.length() ? text2 : text1;
const size_t i = longtext.find(shorttext);
if (i != string_t::npos) {
// Shorter text is inside the longer text (speedup).
const Operation op = (text1.length() > text2.length()) ? DELETE : INSERT;
diffs.push_back(Diff(op, longtext.substr(0, i)));
diffs.push_back(Diff(EQUAL, shorttext));
diffs.push_back(Diff(op, safeMid(longtext, i + shorttext.length())));
return;
}
if (shorttext.length() == 1) {
// Single character string.
// After the previous speedup, the character can't be an equality.
diffs.push_back(Diff(DELETE, text1));
diffs.push_back(Diff(INSERT, text2));
return;
}
// Garbage collect longtext and shorttext by scoping out.
}
// Don't risk returning a non-optimal diff if we have unlimited time.
if (deadline != std::numeric_limits<clock_t>::max()) {
// Check to see if the problem can be split in two.
HalfMatchResult hm;
if (diff_halfMatch(text1, text2, hm)) {
// A half-match was found, sort out the return data.
// Send both pairs off for separate processing.
diff_main(hm.text1_a, hm.text2_a, checklines, deadline, diffs);
diffs.push_back(Diff(EQUAL, hm.mid_common));
Diffs diffs_b;
diff_main(hm.text1_b, hm.text2_b, checklines, deadline, diffs_b);
diffs.splice(diffs.end(), diffs_b);
return;
}
}
// Perform a real diff.
if (checklines && text1.length() > 100 && text2.length() > 100) {
diff_lineMode(text1, text2, deadline, diffs);
return;
}
diff_bisect(text1, text2, deadline, diffs);
}
/**
* Do a quick line-level diff on both strings, then rediff the parts for
* greater accuracy.
* This speedup can produce non-minimal diffs.
* @param text1 Old string to be diffed.
* @param text2 New string to be diffed.
* @param deadline Time when the diff should be complete by.
* @param diffs Linked List of Diff objects.
*/
private:
static void diff_lineMode(string_t text1, string_t text2, clock_t deadline, Diffs& diffs) {
// Scan the text on a line-by-line basis first.
Lines linearray;
diff_linesToChars(text1, text2, linearray);
diff_main(text1, text2, false, deadline, diffs);
// Convert the diff back to original text.
diff_charsToLines(diffs, linearray);
// Eliminate freak matches (e.g. blank lines)
diff_cleanupSemantic(diffs);
// Rediff any replacement blocks, this time character-by-character.
// Add a dummy entry at the end.
diffs.push_back(Diff(EQUAL, string_t()));
int count_delete = 0;
int count_insert = 0;
string_t text_delete;
string_t text_insert;
for (typename Diffs::iterator cur_diff = diffs.begin(); cur_diff != diffs.end(); ++cur_diff) {
switch ((*cur_diff).operation) {
case INSERT:
count_insert++;
text_insert += (*cur_diff).text;
break;
case DELETE:
count_delete++;
text_delete += (*cur_diff).text;
break;
case EQUAL:
// Upon reaching an equality, check for prior redundancies.
if (count_delete >= 1 && count_insert >= 1) {
// Delete the offending records and add the merged ones.
typename Diffs::iterator last = cur_diff;
std::advance(cur_diff, -(count_delete + count_insert));
cur_diff = diffs.erase(cur_diff, last);
Diffs new_diffs;
diff_main(text_delete, text_insert, false, deadline, new_diffs);
diffs.splice(cur_diff++, new_diffs);
--cur_diff;
}
count_insert = 0;
count_delete = 0;
text_delete.clear();
text_insert.clear();
break;
}
}
diffs.pop_back(); // Remove the dummy entry at the end.
}
/**
* Find the 'middle snake' of a diff, split the problem in two
* and return the recursively constructed diff.
* See Myers 1986 paper: An O(ND) Difference Algorithm and Its Variations.
* @param text1 Old string to be diffed.
* @param text2 New string to be diffed.
* @return Linked List of Diff objects.
*/
protected:
static Diffs diff_bisect(const string_t &text1, const string_t &text2, clock_t deadline) {
Diffs diffs;
diff_bisect(text1, text2, deadline, diffs);
return diffs;
}
private:
static void diff_bisect(const string_t &text1, const string_t &text2, clock_t deadline, Diffs& diffs) {
// Cache the text lengths to prevent multiple calls.
const int text1_length = text1.length();
const int text2_length = text2.length();
const int max_d = (text1_length + text2_length + 1) / 2;
const int v_offset = max_d;
const int v_length = 2 * max_d;
std::vector<int> v1(v_length, -1),
v2(v_length, -1);
v1[v_offset + 1] = 0;
v2[v_offset + 1] = 0;
const int delta = text1_length - text2_length;
// If the total number of characters is odd, then the front path will
// collide with the reverse path.
const bool front = (delta % 2 != 0);
// Offsets for start and end of k loop.
// Prevents mapping of space beyond the grid.
int k1start = 0;
int k1end = 0;
int k2start = 0;
int k2end = 0;
for (int d = 0; d < max_d; d++) {
// Bail out if deadline is reached.
if (clock() > deadline) {
break;
}
// Walk the front path one step.
for (int k1 = -d + k1start; k1 <= d - k1end; k1 += 2) {
const int k1_offset = v_offset + k1;
int x1;
if (k1 == -d || (k1 != d && v1[k1_offset - 1] < v1[k1_offset + 1])) {
x1 = v1[k1_offset + 1];
} else {
x1 = v1[k1_offset - 1] + 1;
}
int y1 = x1 - k1;
while (x1 < text1_length && y1 < text2_length
&& text1[x1] == text2[y1]) {
x1++;
y1++;
}
v1[k1_offset] = x1;
if (x1 > text1_length) {
// Ran off the right of the graph.
k1end += 2;
} else if (y1 > text2_length) {
// Ran off the bottom of the graph.
k1start += 2;
} else if (front) {
int k2_offset = v_offset + delta - k1;
if (k2_offset >= 0 && k2_offset < v_length && v2[k2_offset] != -1) {
// Mirror x2 onto top-left coordinate system.
int x2 = text1_length - v2[k2_offset];
if (x1 >= x2) {
// Overlap detected.
diff_bisectSplit(text1, text2, x1, y1, deadline, diffs);
return;
}
}
}
}
// Walk the reverse path one step.
for (int k2 = -d + k2start; k2 <= d - k2end; k2 += 2) {
const int k2_offset = v_offset + k2;
int x2;
if (k2 == -d || (k2 != d && v2[k2_offset - 1] < v2[k2_offset + 1])) {
x2 = v2[k2_offset + 1];
} else {
x2 = v2[k2_offset - 1] + 1;
}
int y2 = x2 - k2;
while (x2 < text1_length && y2 < text2_length
&& text1[text1_length - x2 - 1] == text2[text2_length - y2 - 1]) {
x2++;
y2++;
}
v2[k2_offset] = x2;
if (x2 > text1_length) {
// Ran off the left of the graph.
k2end += 2;
} else if (y2 > text2_length) {
// Ran off the top of the graph.
k2start += 2;
} else if (!front) {
int k1_offset = v_offset + delta - k2;
if (k1_offset >= 0 && k1_offset < v_length && v1[k1_offset] != -1) {
int x1 = v1[k1_offset];
int y1 = v_offset + x1 - k1_offset;
// Mirror x2 onto top-left coordinate system.
x2 = text1_length - x2;
if (x1 >= x2) {
// Overlap detected.
diff_bisectSplit(text1, text2, x1, y1, deadline, diffs);
return;
}
}
}
}
}
// Diff took too long and hit the deadline or
// number of diffs equals number of characters, no commonality at all.
diffs.clear();
diffs.push_back(Diff(DELETE, text1));
diffs.push_back(Diff(INSERT, text2));
}
/**
* Given the location of the 'middle snake', split the diff in two parts
* and recurse.
* @param text1 Old string to be diffed.
* @param text2 New string to be diffed.
* @param x Index of split point in text1.
* @param y Index of split point in text2.
* @param deadline Time at which to bail if not yet complete.
* @param diffs LinkedList of Diff objects.
*/
private:
static void diff_bisectSplit(const string_t &text1, const string_t &text2, int x, int y, clock_t deadline, Diffs& diffs) {
string_t text1a = text1.substr(0, x);
string_t text2a = text2.substr(0, y);
string_t text1b = safeMid(text1, x);
string_t text2b = safeMid(text2, y);
// Compute both diffs serially.
diff_main(text1a, text2a, false, deadline, diffs);
Diffs diffs_b;
diff_main(text1b, text2b, false, deadline, diffs_b);
diffs.splice(diffs.end(), diffs_b);
}
protected:
struct LinePtr : std::pair<typename string_t::const_pointer, size_t> {
LinePtr() {}
LinePtr(typename string_t::const_pointer p, size_t n) : std::pair<typename string_t::const_pointer, size_t>(p, n) {}
bool operator<(const LinePtr& p) const
{ return this->second < p.second? true : this->second > p.second? false : string_t::traits_type::compare(this->first, p.first, this->second) < 0; }
};
struct Lines : std::vector<LinePtr> { string_t text1, text2; };
/**
* Split two texts into a list of strings. Reduce the texts to a string of
* hashes where each Unicode character represents one line.
* @param text1 First string.
* @param text2 Second string.
* @param lineArray Lines object, containing the encoded text1, the
* encoded text2 and the List of pointers to unique strings. The zeroth element
* of the List of unique strings is intentionally blank.
*/
static void diff_linesToChars(string_t &text1, string_t &text2, Lines& lineArray) {
std::map<LinePtr, size_t> lineHash;
lineArray.text1.swap(text1), lineArray.text2.swap(text2);
// e.g. linearray[4] == "Hello\n"
// e.g. linehash.get("Hello\n") == 4
// "\x00" is a valid character, but various debuggers don't like it.
// So we'll insert a junk entry to avoid generating a null character.
text1 = diff_linesToCharsMunge(lineArray.text1, lineHash);
text2 = diff_linesToCharsMunge(lineArray.text2, lineHash);
lineArray.resize(lineHash.size() + 1);
for (typename std::map<LinePtr, size_t>::const_iterator i = lineHash.begin(); i != lineHash.end(); ++i)
lineArray[(*i).second] = (*i).first;
}
/**
* Split a text into a list of pointers to strings. Reduce the texts to a string of
* hashes where each Unicode character represents one line.
* @param text String to encode.
* @param lineHash Map of string pointers to indices.
* @return Encoded string.
*/
private:
static string_t diff_linesToCharsMunge(const string_t &text, std::map<LinePtr, size_t> &lineHash) {
string_t chars;
// Walk the text, pulling out a substring for each line.
// text.split('\n') would temporarily double our memory footprint.
// Modifying text would create many large strings to garbage collect.
typename string_t::size_type lineLen;
for (typename string_t::const_pointer lineStart = text.c_str(), textEnd = lineStart + text.size(); lineStart < textEnd; lineStart += lineLen + 1) {
lineLen = next_token(text, traits::from_wchar(L'\n'), lineStart);
if (lineStart + lineLen == textEnd) --lineLen;
chars += (char_t)(*lineHash.insert(std::make_pair(LinePtr(lineStart, lineLen + 1), lineHash.size() + 1)).first).second;
}
return chars;
}
/**
* Rehydrate the text in a diff from a string of line hashes to real lines of
* text.
* @param diffs LinkedList of Diff objects.
* @param lineArray List of pointers to unique strings.
*/
private:
static void diff_charsToLines(Diffs &diffs, const Lines& lineArray) {
for (typename Diffs::iterator cur_diff = diffs.begin(); cur_diff != diffs.end(); ++cur_diff) {
string_t text;
for (int y = 0; y < (int)(*cur_diff).text.length(); y++) {
const LinePtr& lp = lineArray[static_cast<size_t>((*cur_diff).text[y])];
text.append(lp.first, lp.second);
}
(*cur_diff).text.swap(text);
}
}
/**
* Determine the common prefix of two strings.
* @param text1 First string.
* @param text2 Second string.
* @return The number of characters common to the start of each string.
*/
public:
static int diff_commonPrefix(const string_t &text1, const string_t &text2) {
// Performance analysis: http://neil.fraser.name/news/2007/10/09/
const int n = std::min(text1.length(), text2.length());
for (int i = 0; i < n; i++) {
if (text1[i] != text2[i]) {
return i;
}
}
return n;
}
/**
* Determine the common suffix of two strings.
* @param text1 First string.
* @param text2 Second string.
* @return The number of characters common to the end of each string.
*/
public:
static int diff_commonSuffix(const string_t &text1, const string_t &text2) {
// Performance analysis: http://neil.fraser.name/news/2007/10/09/
const int text1_length = text1.length();
const int text2_length = text2.length();
const int n = std::min(text1_length, text2_length);
for (int i = 1; i <= n; i++) {
if (text1[text1_length - i] != text2[text2_length - i]) {
return i - 1;
}
}
return n;
}
/**
* Determine if the suffix of one string is the prefix of another.
* @param text1 First string.
* @param text2 Second string.
* @return The number of characters common to the end of the first
* string and the start of the second string.
*/
protected:
static int diff_commonOverlap(const string_t &text1, const string_t &text2) {
// Cache the text lengths to prevent multiple calls.
const int text1_length = text1.length();
const int text2_length = text2.length();
// Eliminate the null case.
if (text1_length == 0 || text2_length == 0) {
return 0;
}
// Truncate the longer string.
string_t text1_trunc = text1;
string_t text2_trunc = text2;
if (text1_length > text2_length) {
text1_trunc = right(text1, text2_length);
} else if (text1_length < text2_length) {
text2_trunc = text2.substr(0, text1_length);
}
const int text_length = std::min(text1_length, text2_length);
// Quick check for the worst case.
if (text1_trunc == text2_trunc) {
return text_length;
}
// Start by looking for a single character match
// and increase length until no match is found.
// Performance analysis: http://neil.fraser.name/news/2010/11/04/
int best = 0;
int length = 1;
while (true) {
string_t pattern = right(text1_trunc, length);
size_t found = text2_trunc.find(pattern);
if (found == string_t::npos) {
return best;
}
length += found;
if (found == 0 || right(text1_trunc, length) == text2_trunc.substr(0, length)) {
best = length;
length++;
}
}
}
protected:
struct HalfMatchResult {
string_t text1_a, text1_b, text2_a, text2_b, mid_common;
void swap(HalfMatchResult& hm) {
text1_a.swap(hm.text1_a), text1_b.swap(hm.text1_b), text2_a.swap(hm.text2_a), text2_b.swap(hm.text2_b), mid_common.swap(hm.mid_common);
}
};
/**
* Do the two texts share a substring which is at least half the length of
* the longer text?
* This speedup can produce non-minimal diffs.
* @param text1 First string.
* @param text2 Second string.
* @param hm HalfMatchResult object, containing the prefix of text1, the
* suffix of text1, the prefix of text2, the suffix of text2 and the
* common middle.
* @return Boolean true if there was a match, false otherwise.
*/
static bool diff_halfMatch(const string_t &text1, const string_t &text2, HalfMatchResult& hm) {
const string_t longtext = text1.length() > text2.length() ? text1 : text2;
const string_t shorttext = text1.length() > text2.length() ? text2 : text1;
if (longtext.length() < 4 || shorttext.length() * 2 < longtext.length()) {
return false; // Pointless.
}
HalfMatchResult res1, res2;
// First check if the second quarter is the seed for a half-match.
bool hm1 = diff_halfMatchI(longtext, shorttext,
(longtext.length() + 3) / 4, res1);
// Check again based on the third quarter.
bool hm2 = diff_halfMatchI(longtext, shorttext,
(longtext.length() + 1) / 2, res2);
if (!hm1 && !hm2) {
return false;
} else if (!hm2) {
hm.swap(res1);
} else if (!hm1) {
hm.swap(res2);
} else {
// Both matched. Select the longest.
hm.swap(res1.mid_common.length() > res2.mid_common.length() ? res1 : res2);
}
// A half-match was found, sort out the return data.
if (text1.length() <= text2.length()) {
hm.text1_a.swap(hm.text2_a);
hm.text1_b.swap(hm.text2_b);
}
return true;
}
/**
* Does a substring of shorttext exist within longtext such that the
* substring is at least half the length of longtext?
* @param longtext Longer string.
* @param shorttext Shorter string.
* @param i Start index of quarter length substring within longtext.
* @param best HalfMatchResult object, containing the prefix of longtext, the
* suffix of longtext, the prefix of shorttext, the suffix of shorttext
* and the common middle.
* @return Boolean true if there was a match, false otherwise.
*/
private:
static bool diff_halfMatchI(const string_t &longtext, const string_t &shorttext, int i, HalfMatchResult& best) {
// Start with a 1/4 length substring at position i as a seed.
const string_t seed = safeMid(longtext, i, longtext.length() / 4);
size_t j = string_t::npos;
while ((j = shorttext.find(seed, j + 1)) != string_t::npos) {
const int prefixLength = diff_commonPrefix(safeMid(longtext, i),
safeMid(shorttext, j));
const int suffixLength = diff_commonSuffix(longtext.substr(0, i),
shorttext.substr(0, j));
if ((int)best.mid_common.length() < suffixLength + prefixLength) {
best.mid_common = safeMid(shorttext, j - suffixLength, suffixLength)
+ safeMid(shorttext, j, prefixLength);
best.text1_a = longtext.substr(0, i - suffixLength);
best.text1_b = safeMid(longtext, i + prefixLength);
best.text2_a = shorttext.substr(0, j - suffixLength);
best.text2_b = safeMid(shorttext, j + prefixLength);
}
}
return best.mid_common.length() * 2 >= longtext.length();
}
/**
* Reduce the number of edits by eliminating semantically trivial equalities.
* @param diffs LinkedList of Diff objects.
*/
public:
static void diff_cleanupSemantic(Diffs &diffs) {
if (diffs.empty()) {
return;
}
bool changes = false;
std::vector<typename Diffs::iterator> equalities; // Stack of equalities.
string_t lastequality; // Always equal to equalities.lastElement().text
typename Diffs::iterator cur_diff;
// Number of characters that changed prior to the equality.
int length_insertions1 = 0;
int length_deletions1 = 0;
// Number of characters that changed after the equality.
int length_insertions2 = 0;
int length_deletions2 = 0;
for (cur_diff = diffs.begin(); cur_diff != diffs.end();) {
if ((*cur_diff).operation == EQUAL) {
// Equality found.
equalities.push_back(cur_diff);
length_insertions1 = length_insertions2;
length_deletions1 = length_deletions2;
length_insertions2 = 0;
length_deletions2 = 0;
lastequality = (*cur_diff).text;
} else {
// An insertion or deletion.
if ((*cur_diff).operation == INSERT) {
length_insertions2 += (*cur_diff).text.length();
} else {
length_deletions2 += (*cur_diff).text.length();
}
// Eliminate an equality that is smaller or equal to the edits on both
// sides of it.
if (!lastequality.empty()
&& ((int)lastequality.length()
<= std::max(length_insertions1, length_deletions1))
&& ((int)lastequality.length()
<= std::max(length_insertions2, length_deletions2))) {
// printf("Splitting: '%s'\n", qPrintable(lastequality));
// Walk back to offending equality.
// Change second copy to insert.
(*(cur_diff = equalities.back())).operation = INSERT;
// Duplicate record.
diffs.insert(cur_diff, Diff(DELETE, lastequality));
equalities.pop_back(); // Throw away the equality we just deleted.
if (!equalities.empty()) {
// Throw away the previous equality (it needs to be reevaluated).
equalities.pop_back();
}
length_insertions1 = 0; // Reset the counters.
length_deletions1 = 0;
length_insertions2 = 0;
length_deletions2 = 0;
lastequality = string_t();
changes = true;
if (!equalities.empty())
// There is a safe equality we can fall back to.
cur_diff = equalities.back();
else
{
// There are no previous equalities, walk back to the start.
cur_diff = diffs.begin();
continue;
}
}
}
++cur_diff;
}
// Normalize the diff.
if (changes) {
diff_cleanupMerge(diffs);
}
diff_cleanupSemanticLossless(diffs);
// Find any overlaps between deletions and insertions.
// e.g: <del>abcxxx</del><ins>xxxdef</ins>
// -> <del>abc</del>xxx<ins>def</ins>
// e.g: <del>xxxabc</del><ins>defxxx</ins>
// -> <ins>def</ins>xxx<del>abc</del>
// Only extract an overlap if it is as big as the edit ahead or behind it.
if ((cur_diff = diffs.begin()) != diffs.end()) {
for (typename Diffs::iterator prev_diff = cur_diff; ++cur_diff != diffs.end(); prev_diff = cur_diff) {
if ((*prev_diff).operation == DELETE &&
(*cur_diff).operation == INSERT) {
string_t deletion = (*prev_diff).text;
string_t insertion = (*cur_diff).text;
int overlap_length1 = diff_commonOverlap(deletion, insertion);
int overlap_length2 = diff_commonOverlap(insertion, deletion);
if (overlap_length1 >= overlap_length2) {
if (overlap_length1 >= deletion.size() / 2.0 ||
overlap_length1 >= insertion.size() / 2.0) {
// Overlap found. Insert an equality and trim the surrounding edits.
diffs.insert(cur_diff, Diff(EQUAL, insertion.substr(0, overlap_length1)));
prev_diff->text =
deletion.substr(0, deletion.length() - overlap_length1);
cur_diff->text = safeMid(insertion, overlap_length1);
// diffs.insert inserts the element before the cursor, so there is
// no need to step past the new element.
}
} else {
if (overlap_length2 >= deletion.length() / 2.0 ||
overlap_length2 >= insertion.length() / 2.0) {
// Reverse overlap found.
// Insert an equality and swap and trim the surrounding edits.
diffs.insert(cur_diff, Diff(EQUAL, deletion.substr(0, overlap_length2)));
prev_diff->operation = INSERT;
prev_diff->text =
insertion.substr(0, insertion.length() - overlap_length2);
cur_diff->operation = DELETE;
cur_diff->text = safeMid(deletion, overlap_length2);
// diffs.insert inserts the element before the cursor, so there is
// no need to step past the new element.
}
}
if (++cur_diff == diffs.end()) break;
}
}
}
}
/**
* Look for single edits surrounded on both sides by equalities
* which can be shifted sideways to align the edit to a word boundary.
* e.g: The c<ins>at c</ins>ame. -> The <ins>cat </ins>came.
* @param diffs LinkedList of Diff objects.
*/
public:
static void diff_cleanupSemanticLossless(Diffs &diffs) {
string_t equality1, edit, equality2;