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diff --git a/third_party/aom/tools/intersect-diffs.py b/third_party/aom/tools/intersect-diffs.py
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+++ b/third_party/aom/tools/intersect-diffs.py
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+#!/usr/bin/env python
+##
+## Copyright (c) 2016, Alliance for Open Media. All rights reserved
+##
+## This source code is subject to the terms of the BSD 2 Clause License and
+## the Alliance for Open Media Patent License 1.0. If the BSD 2 Clause License
+## was not distributed with this source code in the LICENSE file, you can
+## obtain it at www.aomedia.org/license/software. If the Alliance for Open
+## Media Patent License 1.0 was not distributed with this source code in the
+## PATENTS file, you can obtain it at www.aomedia.org/license/patent.
+##
+"""Calculates the "intersection" of two unified diffs.
+
+Given two diffs, A and B, it finds all hunks in B that had non-context lines
+in A and prints them to stdout. This is useful to determine the hunks in B that
+are relevant to A. The resulting file can be applied with patch(1) on top of A.
+"""
+
+__author__ = "jkoleszar@google.com"
+
+import sys
+
+import diff
+
+
+def FormatDiffHunks(hunks):
+    """Re-serialize a list of DiffHunks."""
+    r = []
+    last_header = None
+    for hunk in hunks:
+        this_header = hunk.header[0:2]
+        if last_header != this_header:
+            r.extend(hunk.header)
+            last_header = this_header
+        else:
+            r.extend(hunk.header[2])
+        r.extend(hunk.lines)
+        r.append("\n")
+    return "".join(r)
+
+
+def ZipHunks(rhs_hunks, lhs_hunks):
+    """Join two hunk lists on filename."""
+    for rhs_hunk in rhs_hunks:
+        rhs_file = rhs_hunk.right.filename.split("/")[1:]
+
+        for lhs_hunk in lhs_hunks:
+            lhs_file = lhs_hunk.left.filename.split("/")[1:]
+            if lhs_file != rhs_file:
+                continue
+            yield (rhs_hunk, lhs_hunk)
+
+
+def main():
+    old_hunks = [x for x in diff.ParseDiffHunks(open(sys.argv[1], "r"))]
+    new_hunks = [x for x in diff.ParseDiffHunks(open(sys.argv[2], "r"))]
+    out_hunks = []
+
+    # Join the right hand side of the older diff with the left hand side of the
+    # newer diff.
+    for old_hunk, new_hunk in ZipHunks(old_hunks, new_hunks):
+        if new_hunk in out_hunks:
+            continue
+        old_lines = old_hunk.right
+        new_lines = new_hunk.left
+
+        # Determine if this hunk overlaps any non-context line from the other
+        for i in old_lines.delta_line_nums:
+            if i in new_lines:
+                out_hunks.append(new_hunk)
+                break
+
+    if out_hunks:
+        print FormatDiffHunks(out_hunks)
+        sys.exit(1)
+
+if __name__ == "__main__":
+    main()