diff --git a/src/vs/vscode.proposed.d.ts b/src/vs/vscode.proposed.d.ts
index 03dc91cd19e..660e6de1dfa 100644
--- a/src/vs/vscode.proposed.d.ts
+++ b/src/vs/vscode.proposed.d.ts
@@ -154,4 +154,13 @@ declare module 'vscode' {
 		export function getResourceFromURI(uri: Uri): SCMResource | SCMResourceGroup | undefined;
 		export function registerSCMProvider(id: string, provider: SCMProvider): Disposable;
 	}
+
+	export interface LineChange {
+		readonly originalStartLineNumber: number;
+		readonly originalEndLineNumber: number;
+		readonly modifiedStartLineNumber: number;
+		readonly modifiedEndLineNumber: number;
+	}
+
+	export function computeDiff(oneDocument: TextDocument, otherDocument: TextDocument): Thenable<LineChange[]>;
 }
diff --git a/src/vs/workbench/api/node/extHost.api.impl.ts b/src/vs/workbench/api/node/extHost.api.impl.ts
index 4ba4cd1e85d..0d69b51aad9 100644
--- a/src/vs/workbench/api/node/extHost.api.impl.ts
+++ b/src/vs/workbench/api/node/extHost.api.impl.ts
@@ -32,6 +32,7 @@ import { ExtHostEditors } from 'vs/workbench/api/node/extHostEditors';
 import { ExtHostLanguages } from 'vs/workbench/api/node/extHostLanguages';
 import { ExtHostLanguageFeatures } from 'vs/workbench/api/node/extHostLanguageFeatures';
 import { ExtHostApiCommands } from 'vs/workbench/api/node/extHostApiCommands';
+import { computeDiff } from 'vs/workbench/api/node/extHostFunctions';
 import * as extHostTypes from 'vs/workbench/api/node/extHostTypes';
 import URI from 'vs/base/common/uri';
 import Severity from 'vs/base/common/severity';
@@ -490,6 +491,8 @@ export function createApiFactory(initData: IInitData, threadService: IThreadServ
 			Uri: URI,
 			ViewColumn: extHostTypes.ViewColumn,
 			WorkspaceEdit: extHostTypes.WorkspaceEdit,
+			// functions
+			computeDiff
 		};
 	};
 }
diff --git a/src/vs/workbench/api/node/extHostFunctions.ts b/src/vs/workbench/api/node/extHostFunctions.ts
new file mode 100644
index 00000000000..cb21a24ea0e
--- /dev/null
+++ b/src/vs/workbench/api/node/extHostFunctions.ts
@@ -0,0 +1,30 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+'use strict';
+
+import * as vscode from 'vscode';
+import { toThenable } from 'vs/base/common/async';
+import { DiffComputer } from 'vs/editor/common/diff/diffComputer';
+
+function getTextDocumentLines(document: vscode.TextDocument): string[] {
+	const result = [];
+	for (let i = 0; i < document.lineCount; i++) {
+		result.push(document.lineAt(i).text);
+	}
+	return result;
+}
+
+export function computeDiff(oneDocument: vscode.TextDocument, otherDocument: vscode.TextDocument): Thenable<vscode.LineChange[]> {
+	const oneLines = getTextDocumentLines(oneDocument);
+	const otherLines = getTextDocumentLines(otherDocument);
+	const computer = new DiffComputer(oneLines, otherLines, {
+		shouldPostProcessCharChanges: false,
+		shouldIgnoreTrimWhitespace: false, // options?
+		shouldConsiderTrimWhitespaceInEmptyCase: false
+	});
+
+	return toThenable(computer.computeDiff());
+}
\ No newline at end of file