Initial commit - WPinternals 2.6

2026-06-18 21:30:15 +10:00 · 2018-10-25 22:35:49 +02:00
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+//
+// Copyright (c) 2008-2011, Kenneth Bell
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the "Software"),
+// to deal in the Software without restriction, including without limitation
+// the rights to use, copy, modify, merge, publish, distribute, sublicense,
+// and/or sell copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+//
+
+namespace DiscUtils.Compression
+{
+    /// <summary>
+    /// A canonical Huffman tree implementation.
+    /// </summary>
+    /// <remarks>
+    /// A lookup table is created that will take any bit sequence (max tree depth in length),
+    /// indicating the output symbol.  In WIM files, in practice, no chunk exceeds 32768 bytes
+    /// in length, so we often end up generating a bigger lookup table than the data it's
+    /// encoding. This makes for exceptionally fast symbol lookups O(1), but is inefficient
+    /// overall.
+    /// </remarks>
+    internal sealed class HuffmanTree
+    {
+        private int _numBits; // Max bits per symbol
+        private int _numSymbols; // Max symbols
+        private uint[] _lengths;
+        private uint[] _buffer;
+
+        public HuffmanTree(uint[] lengths)
+        {
+            _lengths = lengths;
+            _numSymbols = lengths.Length;
+
+            uint maxLength = 0;
+            for (int i = 0; i < _lengths.Length; ++i)
+            {
+                if (_lengths[i] > maxLength)
+                {
+                    maxLength = _lengths[i];
+                }
+            }
+
+            _numBits = (int)maxLength;
+            _buffer = new uint[1 << _numBits];
+
+            Build();
+        }
+
+        public uint[] Lengths
+        {
+            get
+            {
+                return _lengths;
+            }
+        }
+
+        public uint NextSymbol(BitStream bitStream)
+        {
+            uint symbol = _buffer[bitStream.Peek(_numBits)];
+
+            // We may have over-read, reset bitstream position
+            bitStream.Consume((int)_lengths[symbol]);
+
+            return symbol;
+        }
+
+        private void Build()
+        {
+            int position = 0;
+
+            // For each bit-length...
+            for (int i = 1; i <= _numBits; ++i)
+            {
+                // Check each symbol
+                for (uint symbol = 0; symbol < _numSymbols; ++symbol)
+                {
+                    if (_lengths[symbol] == i)
+                    {
+                        int numToFill = 1 << (_numBits - i);
+                        for (int n = 0; n < numToFill; ++n)
+                        {
+                            _buffer[position + n] = symbol;
+                        }
+
+                        position += numToFill;
+                    }
+                }
+            }
+
+            for (int i = position; i < _buffer.Length; ++i)
+            {
+                _buffer[i] = uint.MaxValue;
+            }
+        }
+    }
+}