REminiscence/unpack.cpp

107 lines
2.2 KiB
C++

/*
* REminiscence - Flashback interpreter
* Copyright (C) 2005-2018 Gregory Montoir (cyx@users.sourceforge.net)
*/
#include "unpack.h"
#include "util.h"
struct UnpackCtx {
int size;
uint32_t crc;
uint32_t bits;
uint8_t *dst;
const uint8_t *src;
};
static bool nextBit(UnpackCtx *uc) {
bool carry = (uc->bits & 1) != 0;
uc->bits >>= 1;
if (uc->bits == 0) {
uc->bits = READ_BE_UINT32(uc->src); uc->src -= 4;
uc->crc ^= uc->bits;
carry = (uc->bits & 1) != 0;
uc->bits = (1 << 31) | (uc->bits >> 1);
}
return carry;
}
static int getBits(UnpackCtx *uc, int count) {
int bits = 0;
for (int i = 0; i < count; ++i) {
bits <<= 1;
if (nextBit(uc)) {
bits |= 1;
}
}
return bits;
}
static void copyLiteral(UnpackCtx *uc, int bitsCount, int len) {
int count = getBits(uc, bitsCount) + len + 1;
uc->size -= count;
if (uc->size < 0) {
count += uc->size;
uc->size = 0;
}
for (int i = 0; i < count; ++i) {
*(uc->dst - i) = (uint8_t)getBits(uc, 8);
}
uc->dst -= count;
}
static void copyReference(UnpackCtx *uc, int bitsCount, int count) {
uc->size -= count;
if (uc->size < 0) {
count += uc->size;
uc->size = 0;
}
const int offset = getBits(uc, bitsCount);
for (int i = 0; i < count; ++i) {
*(uc->dst - i) = *(uc->dst - i + offset);
}
uc->dst -= count;
}
bool delphine_unpack(uint8_t *dst, int dstSize, const uint8_t *src, int srcSize) {
UnpackCtx uc;
uc.src = src + srcSize - 4;
uc.size = READ_BE_UINT32(uc.src); uc.src -= 4;
if (uc.size > dstSize) {
warning("Unexpected unpack size %d, buffer size %d", uc.size, dstSize);
return false;
}
uc.dst = dst + uc.size - 1;
uc.crc = READ_BE_UINT32(uc.src); uc.src -= 4;
uc.bits = READ_BE_UINT32(uc.src); uc.src -= 4;
uc.crc ^= uc.bits;
do {
if (!nextBit(&uc)) {
if (!nextBit(&uc)) {
copyLiteral(&uc, 3, 0);
} else {
copyReference(&uc, 8, 2);
}
} else {
const int code = getBits(&uc, 2);
switch (code) {
case 3:
copyLiteral(&uc, 8, 8);
break;
case 2:
copyReference(&uc, 12, getBits(&uc, 8) + 1);
break;
case 1:
copyReference(&uc, 10, 4);
break;
case 0:
copyReference(&uc, 9, 3);
break;
}
}
} while (uc.size > 0);
assert(uc.size == 0);
return uc.crc == 0;
}