5 files changed, 147 insertions, 3 deletions
diff --git a/configure.py b/configure.py
index 17afea4..be8eea6 100755
--- a/configure.py
+++ b/configure.py
@@ -140,8 +140,9 @@ if platform not in ('mingw'):
     n.newline()
 
 n.comment('Core source files all build into ninja library.')
-for name in ['build', 'build_log', 'clean', 'eval_env', 'graph', 'graphviz',
-             'parsers', 'util', 'stat_cache', 'disk_interface', 'state']:
+for name in ['build', 'build_log', 'clean', 'edit_distance', 'eval_env',
+             'graph', 'graphviz', 'parsers', 'util', 'stat_cache',
+             'disk_interface', 'state']:
     objs += cxx(name)
 if platform == 'mingw':
     objs += cxx('subprocess-win32')
@@ -176,6 +177,7 @@ for name in ['build_log_test',
              'build_test',
              'clean_test',
              'disk_interface_test',
+             'edit_distance_test',
              'eval_env_test',
              'graph_test',
              'parsers_test',
diff --git a/src/edit_distance.cc b/src/edit_distance.cc
new file mode 100644
index 0000000..fe05f64
--- /dev/null
+++ b/src/edit_distance.cc
@@ -0,0 +1,68 @@
+// Copyright 2011 Google Inc. All Rights Reserved.
+//
+// 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.
+
+#include "edit_distance.h"
+
+#include <vector>
+
+#include "string_piece.h"
+
+int EditDistance(const StringPiece& s1,
+                 const StringPiece& s2,
+                 bool allow_replacements,
+                 int max_edit_distance) {
+  // The algorithm implemented below is the "classic"
+  // dynamic-programming algorithm for computing the Levenshtein
+  // distance, which is described here:
+  //
+  //   http://en.wikipedia.org/wiki/Levenshtein_distance
+  //
+  // Although the algorithm is typically described using an m x n
+  // array, only two rows are used at a time, so this implemenation
+  // just keeps two separate vectors for those two rows.
+  int m = s1.len_;
+  int n = s2.len_;
+
+  std::vector<int> previous(n + 1);
+  std::vector<int> current(n + 1);
+
+  for (int i = 0; i <= n; ++i)
+    previous[i] = i;
+
+  for (int y = 1; y <= m; ++y) {
+    current[0] = y;
+    int best_this_row = current[0];
+
+    for (int x = 1; x <= n; ++x) {
+      if (allow_replacements) {
+        current[x] = min(previous[x-1] + (s1.str_[y-1] == s2.str_[x-1] ? 0 : 1),
+                         min(current[x-1], previous[x])+1);
+      }
+      else {
+        if (s1.str_[y-1] == s2.str_[x-1])
+          current[x] = previous[x-1];
+        else
+          current[x] = min(current[x-1], previous[x]) + 1;
+      }
+      best_this_row = min(best_this_row, current[x]);
+    }
+
+    if (max_edit_distance && best_this_row > max_edit_distance)
+      return max_edit_distance + 1;
+
+    current.swap(previous);
+  }
+
+  return previous[n];
+}
diff --git a/src/edit_distance.h b/src/edit_distance.h
new file mode 100644
index 0000000..186a0d7
--- /dev/null
+++ b/src/edit_distance.h
@@ -0,0 +1,25 @@
+// Copyright 2011 Google Inc. All Rights Reserved.
+//
+// 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.
+
+#ifndef NINJA_EDIT_DISTANCE_H_
+#define NINJA_EDIT_DISTANCE_H_
+
+struct StringPiece;
+
+int EditDistance(const StringPiece& s1,
+                 const StringPiece& s2,
+                 bool allow_replacements = true,
+                 int max_edit_distance = 0);
+
+#endif  // NINJA_EDIT_DISTANCE_H_
diff --git a/src/edit_distance_test.cc b/src/edit_distance_test.cc
new file mode 100644
index 0000000..a4c0486
--- /dev/null
+++ b/src/edit_distance_test.cc
@@ -0,0 +1,49 @@
+// Copyright 2011 Google Inc. All Rights Reserved.
+//
+// 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.
+
+#include "edit_distance.h"
+
+#include "string_piece.h"
+#include "test.h"
+
+TEST(EditDistanceTest, TestEmpty) {
+  EXPECT_EQ(5, EditDistance("", "ninja"));
+  EXPECT_EQ(5, EditDistance("ninja", ""));
+  EXPECT_EQ(0, EditDistance("", ""));
+}
+
+TEST(EditDistanceTest, TestMaxDistance) {
+  const bool allow_replacements = true;
+  for (int max_distance = 1; max_distance < 7; ++max_distance) {
+    EXPECT_EQ(max_distance + 1,
+              EditDistance("abcdefghijklmnop", "ponmlkjihgfedcba",
+                           allow_replacements, max_distance));
+  }
+}
+
+TEST(EditDistanceTest, TestAllowReplacements) {
+  bool allow_replacements = true;
+  EXPECT_EQ(1, EditDistance("ninja", "njnja", allow_replacements));
+  EXPECT_EQ(1, EditDistance("njnja", "ninja", allow_replacements));
+
+  allow_replacements = false;
+  EXPECT_EQ(2, EditDistance("ninja", "njnja", allow_replacements));
+  EXPECT_EQ(2, EditDistance("njnja", "ninja", allow_replacements));
+}
+
+TEST(EditDistanceTest, TestBasics) {
+  EXPECT_EQ(0, EditDistance("browser_tests", "browser_tests"));
+  EXPECT_EQ(1, EditDistance("browser_test", "browser_tests"));
+  EXPECT_EQ(1, EditDistance("browser_tests", "browser_test"));
+}
diff --git a/src/string_piece.h b/src/string_piece.h
index 0e55afb..3b94ce3 100644
--- a/src/string_piece.h
+++ b/src/string_piece.h
@@ -48,4 +48,4 @@ struct StringPiece {
   int len_;
 };
 
-#endif  // NINJA_BROWSE_H_
+#endif  // NINJA_STRINGPIECE_H_