140 lines
3.8 KiB
C++
140 lines
3.8 KiB
C++
#pragma once
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#include <queue>
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#include <cstdint>
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namespace acio2emu::detail {
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class InflateTransformer {
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private:
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std::queue<uint8_t> output_;
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uint8_t flags_ = 0, flag_shift_ = 0;
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uint8_t window_[85] = {};
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int window_offset_ = 81;
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enum class inflateStep {
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readFlags,
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processFlags,
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copyStored,
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copyFromWindow,
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} step_ = inflateStep::readFlags;
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void window_put_(uint8_t b) {
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window_[window_offset_++] = b;
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window_offset_ %= sizeof(window_);
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}
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uint8_t window_get_(int offset) {
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return window_[offset % sizeof(window_)];
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}
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public:
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void put(uint8_t b) {
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auto consumed = false;
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while (true) {
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switch (step_) {
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case inflateStep::readFlags:
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if (consumed) {
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// need more data
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return;
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}
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consumed = true;
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flags_ = b;
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flag_shift_ = 0;
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step_ = inflateStep::processFlags;
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break;
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case inflateStep::processFlags:
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// have we processed every flag?
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if (flag_shift_ > 6) {
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step_ = inflateStep::readFlags;
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break;
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}
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if (flags_ & (1 << flag_shift_)) {
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flag_shift_++;
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if (flags_ & (1 << flag_shift_)) {
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// emit 0xAA when both bits are set
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output_.push(0xAA);
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}
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else {
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// copy from the window when only the lower bit is set
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step_ = inflateStep::copyFromWindow;
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}
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}
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else {
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step_ = inflateStep::copyStored;
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}
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flag_shift_++;
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break;
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case inflateStep::copyFromWindow: {
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if (consumed) {
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// need more data
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return;
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}
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consumed = true;
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// determine the match size, default is 2-bytes
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auto offset = b;
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auto size = 2;
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if (offset >= 0xAA) {
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// 4-byte match
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size = 4;
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offset -= 0xAB;
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}
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else if (offset >= 0x55) {
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// 3-byte match
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size = 3;
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offset -= 0x55;
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}
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for (auto i = 0; i < size; i ++) {
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auto cur = window_get_(offset + i);
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window_put_(cur);
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output_.push(cur);
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}
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// continue processing flags
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step_ = inflateStep::processFlags;
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break;
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}
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case inflateStep::copyStored:
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if (consumed) {
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// need more data
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return;
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}
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consumed = true;
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window_put_(b);
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output_.push(b);
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// continue processing flags
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step_ = inflateStep::processFlags;
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break;
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}
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}
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}
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int get() {
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if (output_.empty()) {
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// output queue is empty
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return -1;
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}
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auto b = output_.front();
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output_.pop();
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return b;
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}
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};
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} |