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Documented CineUnpacker class.

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svn-id: r32665
This commit is contained in:
Kari Salminen 2008-06-11 11:06:07 +00:00
parent 42427f9a4e
commit 7186c3bd1b
2 changed files with 47 additions and 17 deletions
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35
engines/cine/unpack.cpp
View File

@ -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);

29
engines/cine/unpack.h
View File

@ -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