mirror of
https://github.com/qpdf/qpdf.git
synced 2024-12-23 03:18:59 +00:00
5d4cad9c02
Significantly improve the code's use of off_t for file offsets, size_t for memory sizes, and integer types in cases where there has to be compatibility with external interfaces. Rework sections of the code that would have prevented qpdf from working on files larger than 2 (or maybe 4) GB in size.
229 lines
4.7 KiB
C++
229 lines
4.7 KiB
C++
#include <qpdf/Pl_LZWDecoder.hh>
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#include <qpdf/QTC.hh>
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#include <stdexcept>
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#include <string.h>
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#include <assert.h>
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Pl_LZWDecoder::Pl_LZWDecoder(char const* identifier, Pipeline* next,
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bool early_code_change) :
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Pipeline(identifier, next),
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code_size(9),
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next(0),
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byte_pos(0),
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bit_pos(0),
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bits_available(0),
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code_change_delta(early_code_change ? 1 : 0),
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eod(false),
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last_code(256)
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{
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memset(buf, 0, 3);
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}
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Pl_LZWDecoder::~Pl_LZWDecoder()
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{
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}
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void
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Pl_LZWDecoder::write(unsigned char* bytes, size_t len)
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{
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for (size_t i = 0; i < len; ++i)
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{
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this->buf[next++] = bytes[i];
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if (this->next == 3)
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{
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this->next = 0;
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}
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this->bits_available += 8;
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if (this->bits_available >= this->code_size)
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{
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sendNextCode();
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}
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}
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}
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void
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Pl_LZWDecoder::finish()
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{
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getNext()->finish();
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}
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void
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Pl_LZWDecoder::sendNextCode()
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{
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int high = this->byte_pos;
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int med = (this->byte_pos + 1) % 3;
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int low = (this->byte_pos + 2) % 3;
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int bits_from_high = 8 - this->bit_pos;
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int bits_from_med = this->code_size - bits_from_high;
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int bits_from_low = 0;
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if (bits_from_med > 8)
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{
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bits_from_low = bits_from_med - 8;
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bits_from_med = 8;
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}
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int high_mask = (1 << bits_from_high) - 1;
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int med_mask = 0xff - ((1 << (8 - bits_from_med)) - 1);
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int low_mask = 0xff - ((1 << (8 - bits_from_low)) - 1);
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int code = 0;
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code += (this->buf[high] & high_mask) << bits_from_med;
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code += ((this->buf[med] & med_mask) >> (8 - bits_from_med));
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if (bits_from_low)
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{
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code <<= bits_from_low;
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code += ((this->buf[low] & low_mask) >> (8 - bits_from_low));
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this->byte_pos = low;
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this->bit_pos = bits_from_low;
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}
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else
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{
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this->byte_pos = med;
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this->bit_pos = bits_from_med;
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}
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if (this->bit_pos == 8)
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{
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this->bit_pos = 0;
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++this->byte_pos;
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this->byte_pos %= 3;
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}
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this->bits_available -= this->code_size;
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handleCode(code);
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}
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unsigned char
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Pl_LZWDecoder::getFirstChar(int code)
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{
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unsigned char result = '\0';
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if (code < 256)
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{
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result = (unsigned char) code;
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}
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else
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{
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assert(code > 257);
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unsigned int idx = code - 258;
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assert(idx < table.size());
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Buffer& b = table[idx];
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result = b.getBuffer()[0];
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}
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return result;
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}
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void
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Pl_LZWDecoder::addToTable(unsigned char next)
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{
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unsigned int last_size = 0;
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unsigned char const* last_data = 0;
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unsigned char tmp[1];
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if (this->last_code < 256)
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{
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tmp[0] = this->last_code;
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last_data = tmp;
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last_size = 1;
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}
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else
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{
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assert(this->last_code > 257);
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unsigned int idx = this->last_code - 258;
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assert(idx < table.size());
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Buffer& b = table[idx];
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last_data = b.getBuffer();
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last_size = (unsigned int) b.getSize();
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}
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Buffer entry(1 + last_size);
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unsigned char* new_data = entry.getBuffer();
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memcpy(new_data, last_data, last_size);
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new_data[last_size] = next;
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this->table.push_back(entry);
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}
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void
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Pl_LZWDecoder::handleCode(int code)
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{
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if (this->eod)
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{
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return;
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}
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if (code == 256)
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{
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if (! this->table.empty())
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{
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QTC::TC("libtests", "Pl_LZWDecoder intermediate reset");
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}
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this->table.clear();
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this->code_size = 9;
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}
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else if (code == 257)
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{
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this->eod = true;
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}
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else
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{
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if (this->last_code != 256)
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{
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// Add to the table from last time. New table entry would
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// be what we read last plus the first character of what
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// we're reading now.
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unsigned char next = '\0';
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unsigned int table_size = (unsigned int) table.size();
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if (code < 256)
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{
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// just read < 256; last time's next was code
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next = code;
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}
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else if (code > 257)
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{
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size_t idx = code - 258;
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if (idx > table_size)
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{
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throw std::runtime_error("LZWDecoder: bad code received");
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}
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else if (idx == table_size)
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{
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// The encoder would have just created this entry,
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// so the first character of this entry would have
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// been the same as the first character of the
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// last entry.
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QTC::TC("libtests", "Pl_LZWDecoder last was table size");
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next = getFirstChar(this->last_code);
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}
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else
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{
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next = getFirstChar(code);
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}
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}
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unsigned int new_idx = 258 + table_size;
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if (new_idx == 4096)
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{
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throw std::runtime_error("LZWDecoder: table full");
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}
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addToTable(next);
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unsigned int change_idx = new_idx + code_change_delta;
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if ((change_idx == 511) ||
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(change_idx == 1023) ||
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(change_idx == 2047))
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{
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++this->code_size;
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}
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}
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if (code < 256)
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{
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unsigned char ch = (unsigned char) code;
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getNext()->write(&ch, 1);
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}
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else
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{
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Buffer& b = table[code - 258];
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getNext()->write(b.getBuffer(), b.getSize());
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}
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}
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this->last_code = code;
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}
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