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[polintos/scott/priv.git] / include / c++ / util / radix.h

diff --git a/include/c++/util/radix.h b/include/c++/util/radix.h
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+++ b/include/c++/util/radix.h
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+// Generic radix trees, which supports mapping integer keys to objects.
+//
+// Written by Scott Wood <scott@buserror.net>.
+// 
+// This software is provided 'as-is', without any express or implied warranty.
+// In no event will the authors or contributors be held liable for any damages
+// arising from the use of this software.
+// 
+// This software is in the public domain.
+
+#ifndef _UTIL_RADIX_H
+#define _UTIL_RADIX_H
+
+#include <assert.h>
+#include <stddef.h>
+#include <stdint.h>
+
+#include <lowlevel/bitops.h>
+
+namespace Util {
+       // Each leaf node in the tree will contain 2**radix_bits handles.
+       // Each directory node will contain 2**dir_bits pointers.
+       template <typename T, int radix_bits, int dir_bits = radix_bits>
+       class RadixTree {
+               typedef unsigned int Key;
+
+               enum {
+                       node_size = 1 << radix_bits,
+                       dir_size = 1 << dir_bits,
+                       long_bits = sizeof(unsigned long) * 8,
+               };
+               
+               struct Node {
+                       const int shift;
+                       
+               protected:
+                       Node(int SHIFT) : shift(SHIFT)
+                       {
+                       }
+               };
+               
+               struct LeafNode : public Node {
+                       T handles[node_size];
+                       
+                       LeafNode() : Node(0)
+                       {
+                               shift = 0;
+                               memset(handles, 0, sizeof(handles));
+                       }
+               };
+               
+               struct DirNode : public Node {
+                       Node *ptrs[node_size];
+
+                       DirNode(int shift) : Node(shift)
+                       {
+                               memset(ptrs, 0, sizeof(ptrs));
+                       }
+               };
+       
+               Node *toplevel;
+               
+               static int key_to_dir_offset(Key key, int shift)
+               {
+                       return (key >> shift) & (dir_size - 1);
+               }
+
+               static uint key_to_offset(Key key)
+               {
+                       return key & (node_size - 1);
+               }
+
+       public:
+               T *lookup(Key key, bool add = false)
+               {
+                       int next_shift = toplevel->shift == 0 ? radix_bits : dir_bits;
+                       
+                       while (unlikely(key_to_dir_offset(key, toplevel->shift +
+                                                              next_shift) != 0))
+                       {
+                               if (!add)
+                                       return NULL;
+                               
+                               Node *new_node = new DirNode(toplevel->shift + next_shift);
+                               new_node->ptrs[0] = toplevel;
+                               toplevel = new_node;
+                               next_shift = dir_bits;
+                       }
+                       
+                       Node *node = toplevel;
+                       
+                       while (node->shift >= radix_bits) {
+                               int off = key_to_dir_offset(key, node->shift);
+                               NodeBase *new_node = node[off];
+                               
+                               shift == 0 ? new LeafNode
+                                                               : new DirNode(shift);
+                               void *new_node = static_cast<void **>(node)[off];
+                               
+                               if (!new_node) {
+                                       if (!add)
+                                               return NULL;
+                                       
+                                       new_node = Mem::alloc_pages(1);
+                                       memset(new_node, 0, Arch::page_size);
+                                       static_cast<void **>(node)[off] = new_node;
+                               }
+                               
+                               shift -= dir_shift;
+                               node = new_node;
+                       }
+                       
+                       assert(shift == 0);
+                       return static_cast<T *>(node) + key_to_offset(key, 0);
+               }
+               
+               RadixTree()
+               {
+                       toplevel = new LeafNode;
+                       memset(toplevel, 0, Arch::page_size);
+                       depth = 0;
+               }
+       };
+}
+
+#endif