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#include <qpdf/Pl_LZWDecoder.hh>
#include <qpdf/QIntC.hh>
#include <qpdf/QTC.hh>
#include <qpdf/Util.hh>
#include <cstring>
#include <stdexcept>
using namespace qpdf;
Pl_LZWDecoder::Pl_LZWDecoder(char const* identifier, Pipeline* next, bool early_code_change) :
Pipeline(identifier, next),
code_change_delta(early_code_change)
{
util::assertion(next, "Attempt to create Pl_LZWDecoder with nullptr as next");
}
void
Pl_LZWDecoder::write(unsigned char const* bytes, size_t len)
{
for (size_t i = 0; i < len; ++i) {
buf[next_char_++] = bytes[i];
if (next_char_ == 3) {
next_char_ = 0;
}
bits_available += 8;
if (bits_available >= code_size) {
sendNextCode();
}
}
}
void
Pl_LZWDecoder::finish()
{
next()->finish();
}
void
Pl_LZWDecoder::sendNextCode()
{
unsigned int high = byte_pos;
unsigned int med = (byte_pos + 1) % 3;
unsigned int low = (byte_pos + 2) % 3;
unsigned int bits_from_high = 8 - bit_pos;
unsigned int bits_from_med = code_size - bits_from_high;
unsigned int bits_from_low = 0;
if (bits_from_med > 8) {
bits_from_low = bits_from_med - 8;
bits_from_med = 8;
}
unsigned int high_mask = (1U << bits_from_high) - 1U;
unsigned int med_mask = 0xff - ((1U << (8 - bits_from_med)) - 1U);
unsigned int low_mask = 0xff - ((1U << (8 - bits_from_low)) - 1U);
unsigned int code = 0;
code += (buf[high] & high_mask) << bits_from_med;
code += ((buf[med] & med_mask) >> (8 - bits_from_med));
if (bits_from_low) {
code <<= bits_from_low;
code += ((buf[low] & low_mask) >> (8 - bits_from_low));
byte_pos = low;
bit_pos = bits_from_low;
} else {
byte_pos = med;
bit_pos = bits_from_med;
}
if (bit_pos == 8) {
bit_pos = 0;
++byte_pos;
byte_pos %= 3;
}
bits_available -= code_size;
handleCode(code);
}
unsigned char
Pl_LZWDecoder::getFirstChar(unsigned int code)
{
if (code < 256) {
return static_cast<unsigned char>(code);
}
util::no_ci_rt_error_if(
code <= 257,
"Pl_LZWDecoder::getFirstChar called with invalid code (" + std::to_string(code) + ")");
unsigned int idx = code - 258;
util::no_ci_rt_error_if(idx >= table.size(), "Pl_LZWDecoder::getFirstChar: table overflow");
Buffer& b = table.at(idx);
return b.getBuffer()[0];
}
void
Pl_LZWDecoder::addToTable(unsigned char c)
{
unsigned int last_size = 0;
unsigned char const* last_data = nullptr;
unsigned char tmp[1];
if (last_code < 256) {
tmp[0] = static_cast<unsigned char>(last_code);
last_data = tmp;
last_size = 1;
} else {
util::no_ci_rt_error_if(
last_code <= 257,
"Pl_LZWDecoder::addToTable called with invalid code (" + std::to_string(last_code) +
")");
unsigned int idx = last_code - 258;
util::no_ci_rt_error_if(idx >= table.size(), "Pl_LZWDecoder::addToTable: table overflow");
Buffer& b = table.at(idx);
last_data = b.getBuffer();
last_size = QIntC::to_uint(b.getSize());
}
Buffer entry(1 + last_size);
unsigned char* new_data = entry.getBuffer();
memcpy(new_data, last_data, last_size);
new_data[last_size] = c;
table.push_back(std::move(entry));
}
void
Pl_LZWDecoder::handleCode(unsigned int code)
{
if (eod) {
return;
}
if (code == 256) {
if (!table.empty()) {
QTC::TC("libtests", "Pl_LZWDecoder intermediate reset");
}
table.clear();
code_size = 9;
} else if (code == 257) {
eod = true;
} else {
if (last_code != 256) {
// Add to the table from last time. New table entry would be what we read last plus the
// first character of what we're reading now.
unsigned char next_c = '\0';
unsigned int table_size = QIntC::to_uint(table.size());
if (code < 256) {
// just read < 256; last time's next_c was code
next_c = static_cast<unsigned char>(code);
} else if (code > 257) {
size_t idx = code - 258;
if (idx > table_size) {
throw std::runtime_error("LZWDecoder: bad code received");
} else if (idx == table_size) {
// The encoder would have just created this entry, so the first character of
// this entry would have been the same as the first character of the last entry.
next_c = getFirstChar(last_code);
} else {
next_c = getFirstChar(code);
}
}
unsigned int new_idx = 258 + table_size;
util::no_ci_rt_error_if(new_idx == 4096, "LZWDecoder: table full");
addToTable(next_c);
unsigned int change_idx = new_idx + code_change_delta;
if (change_idx == 511 || change_idx == 1023 || change_idx == 2047) {
++code_size;
}
}
if (code < 256) {
auto ch = static_cast<unsigned char>(code);
next()->write(&ch, 1);
} else {
unsigned int idx = code - 258;
if (idx >= table.size()) {
throw std::runtime_error("Pl_LZWDecoder::handleCode: table overflow");
}
Buffer& b = table.at(idx);
next()->write(b.getBuffer(), b.getSize());
}
}
last_code = code;
}
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