spicetools/acio2emu/internal/lz.h

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2024-08-28 15:10:34 +00:00
#pragma once
#include <queue>
#include <cstdint>
namespace acio2emu::detail {
class InflateTransformer {
private:
std::queue<uint8_t> output_;
uint8_t flags_ = 0, flag_shift_ = 0;
uint8_t window_[85] = {};
int window_offset_ = 81;
enum class inflateStep {
readFlags,
processFlags,
copyStored,
copyFromWindow,
} step_ = inflateStep::readFlags;
void window_put_(uint8_t b) {
window_[window_offset_++] = b;
window_offset_ %= sizeof(window_);
}
uint8_t window_get_(int offset) {
return window_[offset % sizeof(window_)];
}
public:
void put(uint8_t b) {
auto consumed = false;
while (true) {
switch (step_) {
case inflateStep::readFlags:
if (consumed) {
// need more data
return;
}
consumed = true;
flags_ = b;
flag_shift_ = 0;
step_ = inflateStep::processFlags;
break;
case inflateStep::processFlags:
// have we processed every flag?
if (flag_shift_ > 6) {
step_ = inflateStep::readFlags;
break;
}
if (flags_ & (1 << flag_shift_)) {
flag_shift_++;
if (flags_ & (1 << flag_shift_)) {
// emit 0xAA when both bits are set
output_.push(0xAA);
}
else {
// copy from the window when only the lower bit is set
step_ = inflateStep::copyFromWindow;
}
}
else {
step_ = inflateStep::copyStored;
}
flag_shift_++;
break;
case inflateStep::copyFromWindow: {
if (consumed) {
// need more data
return;
}
consumed = true;
// determine the match size, default is 2-bytes
auto offset = b;
auto size = 2;
if (offset >= 0xAA) {
// 4-byte match
size = 4;
offset -= 0xAB;
}
else if (offset >= 0x55) {
// 3-byte match
size = 3;
offset -= 0x55;
}
for (auto i = 0; i < size; i ++) {
auto cur = window_get_(offset + i);
window_put_(cur);
output_.push(cur);
}
// continue processing flags
step_ = inflateStep::processFlags;
break;
}
case inflateStep::copyStored:
if (consumed) {
// need more data
return;
}
consumed = true;
window_put_(b);
output_.push(b);
// continue processing flags
step_ = inflateStep::processFlags;
break;
}
}
}
int get() {
if (output_.empty()) {
// output queue is empty
return -1;
}
auto b = output_.front();
output_.pop();
return b;
}
};
}