From 3faecf9a00512dcbc8712c4bca9adae72fb64410 Mon Sep 17 00:00:00 2001
From: Kenneth Heafield <github@kheafield.com>
Date: Sat, 12 May 2012 14:01:52 -0400
Subject: Give in and copy bjam into cdec source code

---
 jam-files/boost-build/util/order.py | 121 ++++++++++++++++++++++++++++++++++++
 1 file changed, 121 insertions(+)
 create mode 100644 jam-files/boost-build/util/order.py

(limited to 'jam-files/boost-build/util/order.py')

diff --git a/jam-files/boost-build/util/order.py b/jam-files/boost-build/util/order.py
new file mode 100644
index 00000000..4e67b3f1
--- /dev/null
+++ b/jam-files/boost-build/util/order.py
@@ -0,0 +1,121 @@
+#  Copyright (C) 2003 Vladimir Prus
+#  Use, modification, and distribution is subject to the Boost Software
+#  License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy
+#  at http://www.boost.org/LICENSE_1_0.txt)
+
+class Order:
+    """Allows ordering arbitrary objects with regard to arbitrary binary relation.
+
+        The primary use case is the gcc toolset, which is sensitive to
+        library order: if library 'a' uses symbols from library 'b',
+        then 'a' must be present before 'b' on the linker's command line.
+        
+        This requirement can be lifted for gcc with GNU ld, but for gcc with
+        Solaris LD (and for Solaris toolset as well), the order always matters.
+        
+        So, we need to store order requirements and then order libraries
+        according to them. It it not possible to use dependency graph as
+        order requirements. What we need is "use symbols" relationship
+        while dependency graph provides "needs to be updated" relationship.
+        
+        For example::
+          lib a : a.cpp b;
+          lib b ;
+        
+        For static linking, the 'a' library need not depend on 'b'. However, it
+        still should come before 'b' on the command line.
+    """
+
+    def __init__ (self):
+        self.constraints_ = []
+        
+    def add_pair (self, first, second):
+        """ Adds the constraint that 'first' should precede 'second'.
+        """
+        self.constraints_.append ((first, second))
+
+    def order (self, objects):
+        """ Given a list of objects, reorder them so that the constains specified
+            by 'add_pair' are satisfied.
+            
+            The algorithm was adopted from an awk script by Nikita Youshchenko
+            (yoush at cs dot msu dot su)
+        """
+        # The algorithm used is the same is standard transitive closure,
+        # except that we're not keeping in-degree for all vertices, but
+        # rather removing edges.
+        result = []
+
+        if not objects: 
+            return result
+
+        constraints = self.__eliminate_unused_constraits (objects)
+        
+        # Find some library that nobody depends upon and add it to
+        # the 'result' array.
+        obj = None
+        while objects:
+            new_objects = []
+            while objects:
+                obj = objects [0]
+
+                if self.__has_no_dependents (obj, constraints):
+                    # Emulate break ;
+                    new_objects.extend (objects [1:])
+                    objects = []
+
+                else:
+                    new_objects.append (obj)
+                    obj = None
+                    objects = objects [1:]
+            
+            if not obj:
+                raise BaseException ("Circular order dependencies")
+
+            # No problem with placing first.
+            result.append (obj)
+
+            # Remove all containts where 'obj' comes first,
+            # since they are already satisfied.
+            constraints = self.__remove_satisfied (constraints, obj)
+
+            # Add the remaining objects for further processing
+            # on the next iteration
+            objects = new_objects
+            
+        return result
+
+    def __eliminate_unused_constraits (self, objects):
+        """ Eliminate constraints which mention objects not in 'objects'.
+            In graph-theory terms, this is finding subgraph induced by
+            ordered vertices.
+        """
+        result = []
+        for c in self.constraints_:
+            if c [0] in objects and c [1] in objects:
+                result.append (c)
+
+        return result
+    
+    def __has_no_dependents (self, obj, constraints):
+        """ Returns true if there's no constraint in 'constraints' where 
+            'obj' comes second.
+        """
+        failed = False
+        while constraints and not failed:
+            c = constraints [0]
+
+            if c [1] == obj:
+                failed = True
+
+            constraints = constraints [1:]
+
+        return not failed
+    
+    def __remove_satisfied (self, constraints, obj):
+        result = []
+        for c in constraints:
+            if c [0] != obj:
+                result.append (c)
+
+        return result
-- 
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