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# diff
implementation of myers diff algorithm
[![Build Status](https://travis-ci.org/Swatinem/diff.png?branch=master)](https://travis-ci.org/Swatinem/diff)
[![Coverage Status](https://coveralls.io/repos/Swatinem/diff/badge.png?branch=master)](https://coveralls.io/r/Swatinem/diff)
[![Dependency Status](https://gemnasium.com/Swatinem/diff.png)](https://gemnasium.com/Swatinem/diff)
This uses the [*An O(ND) Difference Algorithm and Its Variations*](http://www.xmailserver.org/diff2.pdf)
Also see http://simplygenius.net/Article/DiffTutorial2 and
http://www.mathertel.de/Diff/ViewSrc.aspx for more inspiration
## Installation
$ npm install diff
$ component install Swatinem/diff
## Usage
### diff(a, b, [eql(a, b)])
Given two arrays (or array-likes, such as strings) `a` and `b` and an optional
equal function `eql`, this will return an array with the following operations:
* *nop* the element is in both arrays
* *ins* the element is only in array `b` and will be inserted
* *del* the element in only in array `a` and will be removed
* *rep* the element from `a` will be replaced by the element from `b`.
This is essentially the same as a del+ins
## License
LGPLv3

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/* vim: set shiftwidth=2 tabstop=2 noexpandtab textwidth=80 wrap : */
"use strict";
module.exports = diff;
function diff(a, b, eql) {
if (!eql)
eql = function (a, b) { return a === b; };
var d = new Diff(a, b, eql);
return d.editscript();
}
diff.Diff = Diff;
function Diff(a, b, eql) {
this.a = a;
this.b = b;
this.eql = eql;
this.moda = Array.apply(null, new Array(a.length)).map(true.valueOf, false);
this.modb = Array.apply(null, new Array(b.length)).map(true.valueOf, false);
// just to save some allocations:
this.down = {};
this.up = {};
this.lcs(0, a.length, 0, b.length);
}
Diff.NOOP = 'nop';
Diff.DELETE = 'del';
Diff.INSERT = 'ins';
Diff.REPLACE = 'rep';
Diff.prototype.editscript = function Diff_editscript() {
var moda = this.moda, modb = this.modb;
var astart = 0, aend = moda.length;
var bstart = 0, bend = modb.length;
var result = [];
while (astart < aend || bstart < bend) {
if (astart < aend && bstart < bend) {
if (!moda[astart] && !modb[bstart]) {
result.push(Diff.NOOP);
astart++; bstart++;
continue;
} else if (moda[astart] && modb[bstart]) {
result.push(Diff.REPLACE);
astart++; bstart++;
continue;
}
}
if (astart < aend && (bstart >= bend || moda[astart])) {
result.push(Diff.DELETE);
astart++;
}
if (bstart < bend && (astart >= aend || modb[bstart])) {
result.push(Diff.INSERT);
bstart++;
}
}
return result;
};
Diff.prototype.lcs = function Diff_lcs(astart, aend, bstart, bend) {
var a = this.a, b = this.b, eql = this.eql;
// separate common head
while (astart < aend && bstart < bend && eql(a[astart], b[bstart])) {
astart++; bstart++;
}
// separate common tail
while (astart < aend && bstart < bend && eql(a[aend - 1], b[bend - 1])) {
aend--; bend--;
}
if (astart === aend) {
// only insertions
while (bstart < bend) {
this.modb[bstart] = true;
bstart++;
}
} else if (bend === bstart) {
// only deletions
while (astart < aend) {
this.moda[astart] = true;
astart++;
}
} else {
var snake = this.snake(astart, aend, bstart, bend);
this.lcs(astart, snake.x, bstart, snake.y);
this.lcs(snake.u, aend, snake.v, bend);
}
};
Diff.prototype.snake = function Diff_snake(astart, aend, bstart, bend) {
var a = this.a, b = this.b, eql = this.eql;
var N = aend - astart,
M = bend - bstart;
var kdown = astart - bstart;
var kup = aend - bend;
var delta = N - M;
var deltaOdd = delta & 1;
var down = this.down;
down[kdown + 1] = astart;
var up = this.up;
up[kup - 1] = aend;
var Dmax = (N + M + 1) / 2;
for (var D = 0; D <= Dmax; D++) {
var k, x, y;
// forward path
for (k = kdown - D; k <= kdown + D; k += 2) {
if (k === kdown - D) {
x = down[k + 1]; // down
} else {
x = down[k - 1] + 1; // right
if ((k < kdown + D) && (down[k + 1] >= x)) {
x = down[k + 1]; // down
}
}
y = x - k;
while (x < aend && y < bend && eql(a[x], b[y])) {
x++; y++; // diagonal
}
down[k] = x;
if (deltaOdd && (kup - D < k) && (k < kup + D) &&
up[k] <= down[k]) {
return {
x: down[k],
y: down[k] - k,
u: up[k],
v: up[k] - k,
};
}
}
// reverse path
for (k = kup - D; k <= kup + D; k += 2) {
if (k === kup + D) {
x = up[k - 1]; // up
} else {
x = up[k + 1] - 1; // left
if ((k > kup - D) && (up[k - 1] < x)) {
x = up[k - 1]; // up
}
}
y = x - k;
while (x > astart && y > bstart && eql(a[x - 1], b[y - 1])) {
x--; y--; // diagonal
}
up[k] = x;
if (!deltaOdd && (kdown - D <= k) && (k <= kdown + D) &&
up[k] <= down[k]) {
return {
x: down[k],
y: down[k] - k,
u: up[k],
v: up[k] - k,
};
}
}
}
};