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author | Kari Salminen | 2008-06-11 11:06:07 +0000 |
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committer | Kari Salminen | 2008-06-11 11:06:07 +0000 |
commit | 7186c3bd1bbb1fa9719ed363380ce961f09f133c (patch) | |
tree | ee8d2d45e3d7f6b0bf63664bdc52337a1832b01d /engines/cine | |
parent | 42427f9a4ec2ec768d355729bbdd77f52ddb37b9 (diff) | |
download | scummvm-rg350-7186c3bd1bbb1fa9719ed363380ce961f09f133c.tar.gz scummvm-rg350-7186c3bd1bbb1fa9719ed363380ce961f09f133c.tar.bz2 scummvm-rg350-7186c3bd1bbb1fa9719ed363380ce961f09f133c.zip |
Documented CineUnpacker class.
svn-id: r32665
Diffstat (limited to 'engines/cine')
-rw-r--r-- | engines/cine/unpack.cpp | 35 | ||||
-rw-r--r-- | engines/cine/unpack.h | 29 |
2 files changed, 47 insertions, 17 deletions
diff --git a/engines/cine/unpack.cpp b/engines/cine/unpack.cpp index 8e775c3632..364331e439 100644 --- a/engines/cine/unpack.cpp +++ b/engines/cine/unpack.cpp @@ -47,10 +47,12 @@ int CineUnpacker::rcr(int inputCarry) { int CineUnpacker::nextBit() { int carry = rcr(0); + // Normally if the chunk becomes zero then the carry is one as + // the end of chunk marker is always the last to be shifted out. if (_chunk32b == 0) { _chunk32b = readSource(); _crc ^= _chunk32b; - carry = rcr(1); + carry = rcr(1); // Put the end of chunk marker in the most significant bit } return carry; } @@ -64,7 +66,7 @@ uint16 CineUnpacker::getBits(byte numBits) { return c; } -void CineUnpacker::unpackBytes(uint16 numBytes) { +void CineUnpacker::unpackRawBytes(uint16 numBytes) { _datasize -= numBytes; while (numBytes--) { *_dst = (byte)getBits(8); @@ -82,31 +84,40 @@ void CineUnpacker::copyRelocatedBytes(uint16 offset, uint16 numBytes) { bool CineUnpacker::unpack(byte *dst, const byte *src, int srcLen) { _src = src + srcLen - 4; - _datasize = readSource(); + _datasize = readSource(); // Unpacked length in bytes _dst = dst + _datasize - 1; _crc = readSource(); _chunk32b = readSource(); _crc ^= _chunk32b; do { - if (!nextBit()) { - if (!nextBit()) { + /* + Bits => Action: + 0 0 => unpackRawBytes(3 bits + 1) i.e. unpackRawBytes(1..9) + 1 1 1 => unpackRawBytes(8 bits + 9) i.e. unpackRawBytes(9..264) + 0 1 => copyRelocatedBytes(8 bits, 2) i.e. copyRelocatedBytes(0..255, 2) + 1 0 0 => copyRelocatedBytes(9 bits, 3) i.e. copyRelocatedBytes(0..511, 3) + 1 0 1 => copyRelocatedBytes(10 bits, 4) i.e. copyRelocatedBytes(0..1023, 4) + 1 1 0 => copyRelocatedBytes(12 bits, 8 bits + 1) i.e. copyRelocatedBytes(0..4095, 1..256) + */ + if (!nextBit()) { // 0... + if (!nextBit()) { // 0 0 uint16 numBytes = getBits(3) + 1; - unpackBytes(numBytes); - } else { + unpackRawBytes(numBytes); + } else { // 0 1 uint16 numBytes = 2; uint16 offset = getBits(8); copyRelocatedBytes(offset, numBytes); } - } else { + } else { // 1... uint16 c = getBits(2); - if (c == 3) { + if (c == 3) { // 1 1 1 uint16 numBytes = getBits(8) + 9; - unpackBytes(numBytes); - } else if (c < 2) { // c == 0 || c == 1 + unpackRawBytes(numBytes); + } else if (c < 2) { // 1 0 x uint16 numBytes = c + 3; uint16 offset = getBits(c + 9); copyRelocatedBytes(offset, numBytes); - } else { // c == 2 + } else { // 1 1 0 uint16 numBytes = getBits(8) + 1; uint16 offset = getBits(12); copyRelocatedBytes(offset, numBytes); diff --git a/engines/cine/unpack.h b/engines/cine/unpack.h index 894d59d0b4..f0a7ee3804 100644 --- a/engines/cine/unpack.h +++ b/engines/cine/unpack.h @@ -31,6 +31,12 @@ namespace Cine { +/** + * A LZ77 style decompressor for Delphine's data files + * used in at least Future Wars and Operation Stealth. + * @note Works backwards in the source and destination buffers. + * @note Can work with source and destination in the same buffer if there's space. + */ class CineUnpacker { public: /** Returns true if unpacking was successful, otherwise false. */ @@ -47,14 +53,27 @@ private: int rcr(int inputCarry); int nextBit(); uint16 getBits(byte numBits); - void unpackBytes(uint16 numBytes); + + /** + * Copy raw bytes from the input stream and write them to the destination stream. + * This is used when no adequately long match is found in the sliding window. + * @param numBytes Amount of bytes to copy from the input stream + */ + void unpackRawBytes(uint16 numBytes); + + /** + * Copy bytes from the sliding window in the destination buffer. + * This is used when a match of two bytes or longer is found. + * @param offset Offset in the sliding window + * @param numBytes Amount of bytes to copy + */ void copyRelocatedBytes(uint16 offset, uint16 numBytes); private: - int _datasize; - uint32 _crc; + int _datasize; //!< Bytes left to write into the unpacked data stream + uint32 _crc; //!< Error-detecting code uint32 _chunk32b; //!< The current internal 32-bit chunk - byte *_dst; - const byte *_src; + byte *_dst; //!< Destination buffer pointer + const byte *_src; //!< Source buffer pointer }; } // End of namespace Cine |