103 lines
2.2 KiB
C++
103 lines
2.2 KiB
C++
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/*
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* REminiscence - Flashback interpreter
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* Copyright (C) 2005-2019 Gregory Montoir (cyx@users.sourceforge.net)
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*/
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#include "unpack.h"
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#include "util.h"
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struct UnpackCtx {
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int size;
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uint32_t crc;
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uint32_t bits;
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uint8_t *dst;
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const uint8_t *src;
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};
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static int nextBit(UnpackCtx *uc) {
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int bit = (uc->bits & 1);
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uc->bits >>= 1;
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if (uc->bits == 0) { // getnextlwd
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const uint32_t bits = READ_BE_UINT32(uc->src); uc->src -= 4;
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uc->crc ^= bits;
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bit = (bits & 1);
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uc->bits = (1 << 31) | (bits >> 1);
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}
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return bit;
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}
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template<int count>
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static uint32_t getBits(UnpackCtx *uc) { // rdd1bits
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uint32_t bits = 0;
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for (int i = 0; i < count; ++i) {
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bits = (bits << 1) | nextBit(uc);
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}
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return bits;
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}
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static void copyLiteral(UnpackCtx *uc, int len) { // getd3chr
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uc->size -= len;
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if (uc->size < 0) {
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len += uc->size;
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uc->size = 0;
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}
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for (int i = 0; i < len; ++i, --uc->dst) {
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*(uc->dst) = (uint8_t)getBits<8>(uc);
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}
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}
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static void copyReference(UnpackCtx *uc, int len, int offset) { // copyd3bytes
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uc->size -= len;
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if (uc->size < 0) {
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len += uc->size;
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uc->size = 0;
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}
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for (int i = 0; i < len; ++i, --uc->dst) {
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*(uc->dst) = *(uc->dst + offset);
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}
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}
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bool bytekiller_unpack(uint8_t *dst, int dstSize, const uint8_t *src, int srcSize) {
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UnpackCtx uc;
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uc.src = src + srcSize - 4;
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uc.size = READ_BE_UINT32(uc.src); uc.src -= 4;
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if (uc.size > dstSize) {
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warning("Unexpected unpack size %d, buffer size %d", uc.size, dstSize);
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return false;
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}
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uc.dst = dst + uc.size - 1;
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uc.crc = READ_BE_UINT32(uc.src); uc.src -= 4;
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uc.bits = READ_BE_UINT32(uc.src); uc.src -= 4;
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uc.crc ^= uc.bits;
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do {
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if (!nextBit(&uc)) {
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if (!nextBit(&uc)) {
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copyLiteral(&uc, getBits<3>(&uc) + 1);
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} else {
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copyReference(&uc, 2, getBits<8>(&uc));
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}
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} else {
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const int code = getBits<2>(&uc);
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switch (code) {
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case 3:
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copyLiteral(&uc, getBits<8>(&uc) + 9);
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break;
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case 2: {
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const int len = getBits<8>(&uc) + 1;
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copyReference(&uc, len, getBits<12>(&uc));
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}
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break;
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case 1:
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copyReference(&uc, 4, getBits<10>(&uc));
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break;
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case 0:
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copyReference(&uc, 3, getBits<9>(&uc));
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break;
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}
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}
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} while (uc.size > 0);
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assert(uc.size == 0);
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return uc.crc == 0;
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}
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