algorithm - LZ77和Direct2编码算法的实现

Question

我需要找到MSDN网站上描述的 LZ77 和 Direct2 算法的实现。我期待它可能是 SDK 的一部分。到目前为止，我没有运气。

有人可以指导我到哪里可以找到这些算法，以便我可以在我的代码中使用它们吗？

谢谢

Answer 1

用 google 进行简单搜索会得到：

• 维基百科 - LZ77 和 LZ78
• DIRECT2 编码算法

我希望你不是要代码本身。

Answer 2

你找到解决办法了吗？我在 Michael Cohen 的帮助下将其翻译成 C# 进行解压。 http://volatility.googlecode.com/svn-history/r1609/branches/scudette/contrib/pyxpress/pyxpress.c

我的测试表明它工作正常，但请为您自己测试:)

    private static int PAGE_SIZE = 0x00001000;
    private static int XPRESS_ENCODE_MAGIC = 0x19880922;
    private static int DELTA_PAGE = ((2 * PAGE_SIZE) - 1);
    private static int UNCOMPRESSED_BLOCK_SIZE = (PAGE_SIZE * 0x10);



    public static byte[] Xpress_Decompress(byte[] inputBuffer, int outputSize)
    {
        int outputIndex, inputIndex;
        int indicator, indicatorBit;
        int length;
        int offset;
        int nibbleIndex;
        int nibbleIndicator;
        int inputSize = inputBuffer.Length;

        outputIndex = 0;
        inputIndex = 0;
        indicator = 0;
        indicatorBit = 0;
        length = 0;
        offset = 0;
        nibbleIndex = 0;
        nibbleIndicator = XPRESS_ENCODE_MAGIC;

        var outputBuffer = new byte[outputSize];
        while ((outputIndex < outputSize) && (inputIndex < inputSize))
        {
            if (indicatorBit == 0)
            {
                if (inputIndex + 3 >= inputSize) goto Done;
                indicator = GetInt(inputBuffer, inputIndex);
                inputIndex += sizeof(int);
                indicatorBit = 32;
            }
            indicatorBit--;

            //* check whether the bit specified by IndicatorBit is set or not
            //* set in Indicator. For example, if IndicatorBit has value 4
            //* check whether the 4th bit of the value in Indicator is set

            if (((indicator >> indicatorBit) & 1) == 0)
            {
                if (outputIndex >= outputSize) 
                    goto Done;
                outputBuffer[outputIndex] = inputBuffer[inputIndex];
                inputIndex += sizeof(byte);
                outputIndex += sizeof(byte);
            }
            else
            {
                if (inputIndex + 1 >= inputSize) 
                    goto Done;
                length = (inputBuffer[inputIndex + 1] << 8) | inputBuffer[inputIndex];

                /*
                if ((OutputIndex > 0xD0) && (OutputIndex < 0xF0))
                {
                    printf("DECOMP: READ AT [0x%08X] = %04X \n", InputIndex, Length);
                }
                */
                inputIndex += sizeof(ushort);
                offset = length / 8;
                length = length % 8;
                //if ((OutputIndex > 0xD0) && (OutputIndex < 0xF0)) printf("--1 Len: %02X (%d)\n", Length, Length);
                if (length == 7)
                {
                    if (nibbleIndex == 0)
                    {
                        nibbleIndex = inputIndex;
                        if (inputIndex >= inputSize) 
                            goto Done;
                        length = inputBuffer[inputIndex] % 16;
                        //if ((OutputIndex > 0xD0) && (OutputIndex < 0xF0)) printf("--2 Len: %02X (%d)\n", Length, Length);
                        inputIndex += sizeof(byte);
                    }
                    else
                    {
                        length = inputBuffer[nibbleIndex] / 16;
                        //if ((OutputIndex > 0xD0) && (OutputIndex < 0xF0)) printf("--3 Len: %02X (%d)\n", Length, Length);
                        nibbleIndex = 0;
                    }

                    if (length == 15)
                    {
                        if (inputIndex >= inputSize) goto Done;
                        length = inputBuffer[inputIndex];
                        //if ((OutputIndex > 0xD0) && (OutputIndex < 0xF0)) printf("--4 Len: %02X (%d)\n", Length, Length);
                        inputIndex += sizeof(byte);
                        if (length == 255)
                        {
                            if (inputIndex + 2 >= inputSize) goto Done;
                            length = (inputBuffer[inputIndex + 1] << 8) | inputBuffer[inputIndex];
                            inputIndex += sizeof(ushort);
                            length -= (15 + 7);
                        }
                        length += 15;
                        //if ((OutputIndex > 0xD0) && (OutputIndex < 0xF0)) printf("--5 Len: %02X (%d)\n", Length, Length);
                    }
                    length += 7;
                    //if ((OutputIndex > 0xD0) && (OutputIndex < 0xF0)) printf("--6 Len: %02X (%d)\n", Length, Length);
                }

                length += 3;
                //if ((OutputIndex > 0xD0) && (OutputIndex < 0xF0)) printf("--7 Len: %02X (%d)\n", Length, Length);
                //if (Length > 280) printf("DECOMP DEBUG: [0x%08X]->[0x%08X] Len: %d Offset: %08X\n",
                //    OutputIndex, InputIndex, Length, Offset);
                while (length != 0)
                {
                    if ((outputIndex >= outputSize) || ((offset + 1) >= outputIndex)) break;
                    outputBuffer[outputIndex] = outputBuffer[outputIndex - offset - 1];
                    outputIndex += sizeof(byte);
                    length -= sizeof(byte);
                }
            }

        }

    Done:

        if (outputIndex < outputBuffer.Length)
        {
            var buffer = new byte[outputIndex];
            Buffer.BlockCopy(outputBuffer, 0, buffer, 0, outputIndex);
            outputBuffer = buffer;
        }


        return outputBuffer;
    }

    public static int GetInt(byte[] buffer, int offset)
    {
        return
            ((int)buffer[offset]) |
            ((int)buffer[offset + 1] << 8) |
            ((int)buffer[offset + 2] << 16) |
            ((int)buffer[offset + 3] << 24);
    }