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diff --git a/bestflags/flags_util.py b/bestflags/flags_util.py
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+++ b/bestflags/flags_util.py
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+# Copyright (c) 2013 The Chromium OS Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+"""Utility functions to explore the neighbor flags.
+
+Part of the Chrome build flags optimization.
+"""
+
+__author__ = 'yuhenglong@google.com (Yuheng Long)'
+
+import flags
+from flags import Flag
+
+
+def ClimbNext(flags_dict, climb_spec):
+  """Get the flags that are different from |flags_dict| by |climb_spec|.
+
+  Given a set of flags, |flags_dict|, return a new set of flags that are
+  adjacent along the flag spec |climb_spec|.
+
+  An example flags_dict is {foo=[1-9]:foo=5, bar=[1-5]:bar=2} and climb_spec is
+  bar=[1-5]. This method changes the flag that contains the spec bar=[1-5]. The
+  results are its neighbors dictionaries, i.e., {foo=[1-9]:foo=5,
+  bar=[1-5]:bar=1} and {foo=[1-9]:foo=5, bar=[1-5]:bar=3}.
+
+  Args:
+    flags_dict: The dictionary containing the original flags whose neighbors are
+      to be explored.
+    climb_spec: The spec in the flags_dict is to be changed. The spec is a
+      definition in the little language, a string with escaped sequences of the
+      form [<start>-<end>] where start and end is an positive integer for a
+      fillable value. An example of a spec is "foo[0-9]".
+
+  Returns:
+    List of dictionaries of neighbor flags.
+  """
+
+  # This method searches for a pattern [start-end] in the spec. If the spec
+  # contains this pattern, it is a numeric flag. Otherwise it is a boolean flag.
+  # For example, -finline-limit=[1-1000] is a numeric flag and -falign-jumps is
+  # a boolean flag.
+  numeric_flag_match = flags.Search(climb_spec)
+
+  # If the flags do not contain the spec.
+  if climb_spec not in flags_dict:
+    results = flags_dict.copy()
+
+    if numeric_flag_match:
+      # Numeric flags.
+      results[climb_spec] = Flag(climb_spec,
+                                 int(numeric_flag_match.group('start')))
+    else:
+      # Boolean flags.
+      results[climb_spec] = Flag(climb_spec)
+
+    return [results]
+
+  # The flags contain the spec.
+  if not numeric_flag_match:
+    # Boolean flags.
+    results = flags_dict.copy()
+
+    # Turn off the flag. A flag is turned off if it is not presented in the
+    # flags_dict.
+    del results[climb_spec]
+    return [results]
+
+  # Numeric flags.
+  flag = flags_dict[climb_spec]
+
+  # The value of the flag having spec.
+  value = flag.GetValue()
+  results = []
+
+  if value + 1 < int(numeric_flag_match.group('end')):
+    # If the value is not the end value, explore the value that is 1 larger than
+    # the current value.
+    neighbor = flags_dict.copy()
+    neighbor[climb_spec] = Flag(climb_spec, value + 1)
+    results.append(neighbor)
+
+  if value > int(numeric_flag_match.group('start')):
+    # If the value is not the start value, explore the value that is 1 lesser
+    # than the current value.
+    neighbor = flags_dict.copy()
+    neighbor[climb_spec] = Flag(climb_spec, value - 1)
+    results.append(neighbor)
+  else:
+    # Delete the value, i.e., turn off the flag. A flag is turned off if it is
+    # not presented in the flags_dict.
+    neighbor = flags_dict.copy()
+    del neighbor[climb_spec]
+    results.append(neighbor)
+
+  return results