Library import 16 (#2433)

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1 files changed, 121 insertions, 0 deletions

diff --git a/contrib/tools/python3/Modules/rotatingtree.c b/contrib/tools/python3/Modules/rotatingtree.c
new file mode 100644
index 0000000000..07e08bc316
--- /dev/null
+++ b/contrib/tools/python3/Modules/rotatingtree.c
@@ -0,0 +1,121 @@
+#include "rotatingtree.h"
+
+#define KEY_LOWER_THAN(key1, key2)  ((char*)(key1) < (char*)(key2))
+
+/* The randombits() function below is a fast-and-dirty generator that
+ * is probably irregular enough for our purposes.  Note that it's biased:
+ * I think that ones are slightly more probable than zeroes.  It's not
+ * important here, though.
+ */
+
+static unsigned int random_value = 1;
+static unsigned int random_stream = 0;
+
+static int
+randombits(int bits)
+{
+    int result;
+    if (random_stream < (1U << bits)) {
+        random_value *= 1082527;
+        random_stream = random_value;
+    }
+    result = random_stream & ((1<<bits)-1);
+    random_stream >>= bits;
+    return result;
+}
+
+
+/* Insert a new node into the tree.
+   (*root) is modified to point to the new root. */
+void
+RotatingTree_Add(rotating_node_t **root, rotating_node_t *node)
+{
+    while (*root != NULL) {
+        if (KEY_LOWER_THAN(node->key, (*root)->key))
+            root = &((*root)->left);
+        else
+            root = &((*root)->right);
+    }
+    node->left = NULL;
+    node->right = NULL;
+    *root = node;
+}
+
+/* Locate the node with the given key.  This is the most complicated
+   function because it occasionally rebalances the tree to move the
+   resulting node closer to the root. */
+rotating_node_t *
+RotatingTree_Get(rotating_node_t **root, void *key)
+{
+    if (randombits(3) != 4) {
+        /* Fast path, no rebalancing */
+        rotating_node_t *node = *root;
+        while (node != NULL) {
+            if (node->key == key)
+                return node;
+            if (KEY_LOWER_THAN(key, node->key))
+                node = node->left;
+            else
+                node = node->right;
+        }
+        return NULL;
+    }
+    else {
+        rotating_node_t **pnode = root;
+        rotating_node_t *node = *pnode;
+        rotating_node_t *next;
+        int rotate;
+        if (node == NULL)
+            return NULL;
+        while (1) {
+            if (node->key == key)
+                return node;
+            rotate = !randombits(1);
+            if (KEY_LOWER_THAN(key, node->key)) {
+                next = node->left;
+                if (next == NULL)
+                    return NULL;
+                if (rotate) {
+                    node->left = next->right;
+                    next->right = node;
+                    *pnode = next;
+                }
+                else
+                    pnode = &(node->left);
+            }
+            else {
+                next = node->right;
+                if (next == NULL)
+                    return NULL;
+                if (rotate) {
+                    node->right = next->left;
+                    next->left = node;
+                    *pnode = next;
+                }
+                else
+                    pnode = &(node->right);
+            }
+            node = next;
+        }
+    }
+}
+
+/* Enumerate all nodes in the tree.  The callback enumfn() should return
+   zero to continue the enumeration, or non-zero to interrupt it.
+   A non-zero value is directly returned by RotatingTree_Enum(). */
+int
+RotatingTree_Enum(rotating_node_t *root, rotating_tree_enum_fn enumfn,
+                  void *arg)
+{
+    int result;
+    rotating_node_t *node;
+    while (root != NULL) {
+        result = RotatingTree_Enum(root->left, enumfn, arg);
+        if (result != 0) return result;
+        node = root->right;
+        result = enumfn(root, arg);
+        if (result != 0) return result;
+        root = node;
+    }
+    return 0;
+}