107 lines
2.2 KiB
C++
107 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 bool nextBit(UnpackCtx *uc) {
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bool carry = (uc->bits & 1) != 0;
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uc->bits >>= 1;
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if (uc->bits == 0) { // getnextlwd
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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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carry = (uc->bits & 1) != 0;
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uc->bits = (1 << 31) | (uc->bits >> 1);
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}
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return carry;
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}
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static int getBits(UnpackCtx *uc, int count) { // rdd1bits
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int bits = 0;
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for (int i = 0; i < count; ++i) {
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bits <<= 1;
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if (nextBit(uc)) {
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bits |= 1;
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}
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}
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return bits;
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}
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static void copyLiteral(UnpackCtx *uc, int bitsCount, int len) { // getd3chr
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int count = getBits(uc, bitsCount) + len + 1;
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uc->size -= count;
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if (uc->size < 0) {
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count += uc->size;
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uc->size = 0;
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}
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for (int i = 0; i < count; ++i) {
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*(uc->dst - i) = (uint8_t)getBits(uc, 8);
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}
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uc->dst -= count;
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}
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static void copyReference(UnpackCtx *uc, int bitsCount, int count) { // copyd3bytes
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uc->size -= count;
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if (uc->size < 0) {
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count += uc->size;
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uc->size = 0;
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}
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const int offset = getBits(uc, bitsCount);
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for (int i = 0; i < count; ++i) {
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*(uc->dst - i) = *(uc->dst - i + offset);
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}
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uc->dst -= count;
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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, 3, 0);
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} else {
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copyReference(&uc, 8, 2);
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}
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} else {
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const int code = getBits(&uc, 2);
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switch (code) {
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case 3:
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copyLiteral(&uc, 8, 8);
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break;
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case 2:
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copyReference(&uc, 12, getBits(&uc, 8) + 1);
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break;
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case 1:
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copyReference(&uc, 10, 4);
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break;
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case 0:
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copyReference(&uc, 9, 3);
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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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