Pl_LZWDecoder.cc
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#include <qpdf/Pl_LZWDecoder.hh>
#include <qpdf/QIntC.hh>
#include <qpdf/QTC.hh>
#include <qpdf/QUtil.hh>
#include <stdexcept>
#include <string.h>
Pl_LZWDecoder::Pl_LZWDecoder(
char const* identifier, Pipeline* next, bool early_code_change) :
Pipeline(identifier, next),
code_size(9),
next(0),
byte_pos(0),
bit_pos(0),
bits_available(0),
code_change_delta(early_code_change ? 1 : 0),
eod(false),
last_code(256)
{
memset(buf, 0, 3);
}
void
Pl_LZWDecoder::write(unsigned char const* bytes, size_t len)
{
for (size_t i = 0; i < len; ++i) {
this->buf[next++] = bytes[i];
if (this->next == 3) {
this->next = 0;
}
this->bits_available += 8;
if (this->bits_available >= this->code_size) {
sendNextCode();
}
}
}
void
Pl_LZWDecoder::finish()
{
getNext()->finish();
}
void
Pl_LZWDecoder::sendNextCode()
{
unsigned int high = this->byte_pos;
unsigned int med = (this->byte_pos + 1) % 3;
unsigned int low = (this->byte_pos + 2) % 3;
unsigned int bits_from_high = 8 - this->bit_pos;
unsigned int bits_from_med = this->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 += (this->buf[high] & high_mask) << bits_from_med;
code += ((this->buf[med] & med_mask) >> (8 - bits_from_med));
if (bits_from_low) {
code <<= bits_from_low;
code += ((this->buf[low] & low_mask) >> (8 - bits_from_low));
this->byte_pos = low;
this->bit_pos = bits_from_low;
} else {
this->byte_pos = med;
this->bit_pos = bits_from_med;
}
if (this->bit_pos == 8) {
this->bit_pos = 0;
++this->byte_pos;
this->byte_pos %= 3;
}
this->bits_available -= this->code_size;
handleCode(code);
}
unsigned char
Pl_LZWDecoder::getFirstChar(unsigned int code)
{
unsigned char result = '\0';
if (code < 256) {
result = static_cast<unsigned char>(code);
} else if (code > 257) {
unsigned int idx = code - 258;
if (idx >= table.size()) {
throw std::runtime_error(
"Pl_LZWDecoder::getFirstChar: table overflow");
}
Buffer& b = table.at(idx);
result = b.getBuffer()[0];
} else {
throw std::runtime_error(
"Pl_LZWDecoder::getFirstChar called with invalid code (" +
QUtil::int_to_string(code) + ")");
}
return result;
}
void
Pl_LZWDecoder::addToTable(unsigned char next)
{
unsigned int last_size = 0;
unsigned char const* last_data = 0;
unsigned char tmp[1];
if (this->last_code < 256) {
tmp[0] = static_cast<unsigned char>(this->last_code);
last_data = tmp;
last_size = 1;
} else if (this->last_code > 257) {
unsigned int idx = this->last_code - 258;
if (idx >= table.size()) {
throw std::runtime_error(
"Pl_LZWDecoder::addToTable: table overflow");
}
Buffer& b = table.at(idx);
last_data = b.getBuffer();
last_size = QIntC::to_uint(b.getSize());
} else {
throw std::runtime_error(
"Pl_LZWDecoder::addToTable called with invalid code (" +
QUtil::int_to_string(this->last_code) + ")");
}
Buffer entry(1 + last_size);
unsigned char* new_data = entry.getBuffer();
memcpy(new_data, last_data, last_size);
new_data[last_size] = next;
this->table.push_back(entry);
}
void
Pl_LZWDecoder::handleCode(unsigned int code)
{
if (this->eod) {
return;
}
if (code == 256) {
if (!this->table.empty()) {
QTC::TC("libtests", "Pl_LZWDecoder intermediate reset");
}
this->table.clear();
this->code_size = 9;
} else if (code == 257) {
this->eod = true;
} else {
if (this->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 = '\0';
unsigned int table_size = QIntC::to_uint(table.size());
if (code < 256) {
// just read < 256; last time's next was code
next = 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.
QTC::TC("libtests", "Pl_LZWDecoder last was table size");
next = getFirstChar(this->last_code);
} else {
next = getFirstChar(code);
}
}
unsigned int new_idx = 258 + table_size;
if (new_idx == 4096) {
throw std::runtime_error("LZWDecoder: table full");
}
addToTable(next);
unsigned int change_idx = new_idx + code_change_delta;
if ((change_idx == 511) || (change_idx == 1023) ||
(change_idx == 2047)) {
++this->code_size;
}
}
if (code < 256) {
unsigned char ch = static_cast<unsigned char>(code);
getNext()->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);
getNext()->write(b.getBuffer(), b.getSize());
}
}
this->last_code = code;
}