mirror of
https://github.com/fallout2-ce/fallout2-ce.git
synced 2026-07-27 16:47:11 -07:00
245 lines
7.5 KiB
C++
245 lines
7.5 KiB
C++
// NOTE: Functions in these module are somewhat different from what can be seen
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// in IDA because of two new helper functions that deal with incoming bits. I
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// bet something like these were implemented via function-like macro in the
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// same manner zlib deals with bits. The pattern is so common in this module so
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// I made an exception and extracted it into separate functions to increase
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// readability.
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#include "fo1_dat_lzss.h"
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#include <string.h>
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namespace fallout {
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static inline bool lzss_fill_decode_buffer(FILE* stream);
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static inline bool lzss_read_decode_byte(FILE* stream, unsigned char* value);
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static inline bool lzss_decode_chunk_to_buf(unsigned int type, FILE* stream, unsigned char** dest, unsigned int* length);
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constexpr size_t lzssDecodeBufferSize = 1024;
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constexpr unsigned int lzssRingBufferSize = 4116;
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constexpr unsigned int lzssRingBufferMask = 0xFFF;
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constexpr unsigned int lzssDecodeTriggerWindow = 16;
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constexpr unsigned int lzssMatchLengthBias = 3;
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constexpr unsigned char lzssInitialRingFill = ' ';
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constexpr int lzssInitialRingIndex = 4078;
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// 0x6B0860
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static unsigned char decode_buffer[lzssDecodeBufferSize];
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// 0x6B0C60
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static unsigned char* decode_buffer_position;
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// 0x6B0C64
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static unsigned int decode_bytes_left;
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// 0x6B0C68
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static int ring_buffer_index;
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// 0x6B0C6C
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static unsigned char* decode_buffer_end;
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// 0x6B0C70
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static unsigned char ring_buffer[lzssRingBufferSize];
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// 0x4CA260
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int lzss_decode_to_buf(FILE* in, unsigned char* dest, unsigned int length)
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{
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unsigned char* curr;
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unsigned char byte;
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curr = dest;
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memset(ring_buffer, lzssInitialRingFill, lzssInitialRingIndex);
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ring_buffer_index = lzssInitialRingIndex;
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decode_buffer_end = decode_buffer;
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decode_buffer_position = decode_buffer;
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decode_bytes_left = length;
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while (length > 16) {
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if (!lzss_read_decode_byte(in, &byte)) {
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return -1;
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}
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length -= 1;
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if (!lzss_decode_chunk_to_buf(byte & 0x01, in, &curr, &length)) return -1;
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if (!lzss_decode_chunk_to_buf(byte & 0x02, in, &curr, &length)) return -1;
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if (!lzss_decode_chunk_to_buf(byte & 0x04, in, &curr, &length)) return -1;
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if (!lzss_decode_chunk_to_buf(byte & 0x08, in, &curr, &length)) return -1;
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if (!lzss_decode_chunk_to_buf(byte & 0x10, in, &curr, &length)) return -1;
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if (!lzss_decode_chunk_to_buf(byte & 0x20, in, &curr, &length)) return -1;
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if (!lzss_decode_chunk_to_buf(byte & 0x40, in, &curr, &length)) return -1;
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if (!lzss_decode_chunk_to_buf(byte & 0x80, in, &curr, &length)) return -1;
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}
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do {
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if (length == 0) break;
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if (!lzss_read_decode_byte(in, &byte)) {
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return -1;
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}
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length -= 1;
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if (length == 0) break;
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if (!lzss_decode_chunk_to_buf(byte & 0x01, in, &curr, &length)) return -1;
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if (length == 0) break;
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if (!lzss_decode_chunk_to_buf(byte & 0x02, in, &curr, &length)) return -1;
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if (length == 0) break;
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if (!lzss_decode_chunk_to_buf(byte & 0x04, in, &curr, &length)) return -1;
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if (length == 0) break;
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if (!lzss_decode_chunk_to_buf(byte & 0x08, in, &curr, &length)) return -1;
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if (length == 0) break;
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if (!lzss_decode_chunk_to_buf(byte & 0x10, in, &curr, &length)) return -1;
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if (length == 0) break;
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if (!lzss_decode_chunk_to_buf(byte & 0x20, in, &curr, &length)) return -1;
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if (length == 0) break;
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if (!lzss_decode_chunk_to_buf(byte & 0x40, in, &curr, &length)) return -1;
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if (length == 0) break;
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if (!lzss_decode_chunk_to_buf(byte & 0x80, in, &curr, &length)) return -1;
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if (length == 0) break;
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if (!lzss_read_decode_byte(in, &byte)) {
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return -1;
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}
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length -= 1;
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if (length == 0) break;
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if (!lzss_decode_chunk_to_buf(byte & 0x01, in, &curr, &length)) return -1;
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if (length == 0) break;
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if (!lzss_decode_chunk_to_buf(byte & 0x02, in, &curr, &length)) return -1;
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if (length == 0) break;
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if (!lzss_decode_chunk_to_buf(byte & 0x04, in, &curr, &length)) return -1;
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if (length == 0) break;
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if (!lzss_decode_chunk_to_buf(byte & 0x08, in, &curr, &length)) return -1;
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if (length == 0) break;
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if (!lzss_decode_chunk_to_buf(byte & 0x10, in, &curr, &length)) return -1;
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if (length == 0) break;
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if (!lzss_decode_chunk_to_buf(byte & 0x20, in, &curr, &length)) return -1;
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if (length == 0) break;
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if (!lzss_decode_chunk_to_buf(byte & 0x40, in, &curr, &length)) return -1;
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if (length == 0) break;
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if (!lzss_decode_chunk_to_buf(byte & 0x80, in, &curr, &length)) return -1;
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} while (0);
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return curr - dest;
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}
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static inline bool lzss_fill_decode_buffer(FILE* stream)
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{
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size_t bytes_to_read;
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size_t bytes_read;
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if (decode_bytes_left != 0 && decode_buffer_end - decode_buffer_position <= lzssDecodeTriggerWindow) {
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if (decode_buffer_position == decode_buffer_end) {
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decode_buffer_end = decode_buffer;
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} else {
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memmove(decode_buffer, decode_buffer_position, decode_buffer_end - decode_buffer_position);
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decode_buffer_end = decode_buffer + (decode_buffer_end - decode_buffer_position);
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}
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decode_buffer_position = decode_buffer;
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bytes_to_read = lzssDecodeBufferSize - (decode_buffer_end - decode_buffer);
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if (bytes_to_read > decode_bytes_left) {
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bytes_to_read = decode_bytes_left;
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}
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if (bytes_to_read == 0) {
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return false;
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}
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bytes_read = fread(decode_buffer_end, 1, bytes_to_read, stream);
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if (bytes_read != bytes_to_read) {
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return false;
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}
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decode_buffer_end += bytes_read;
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decode_bytes_left -= bytes_read;
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}
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return true;
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}
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static inline bool lzss_read_decode_byte(FILE* stream, unsigned char* value)
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{
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if (!lzss_fill_decode_buffer(stream)) {
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return false;
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}
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if (decode_buffer_position >= decode_buffer_end) {
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return false;
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}
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*value = *decode_buffer_position++;
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return true;
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}
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static inline bool lzss_decode_chunk_to_buf(unsigned int type, FILE* stream, unsigned char** dest, unsigned int* length)
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{
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unsigned char low;
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unsigned char high;
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int dict_offset;
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int dict_index;
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int chunk_length;
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int index;
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if (type != 0) {
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if (*length < 1) {
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return false;
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}
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unsigned char byte;
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if (!lzss_read_decode_byte(stream, &byte)) {
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return false;
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}
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*length -= 1;
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*(*dest) = byte;
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ring_buffer[ring_buffer_index] = *(*dest)++;
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ring_buffer_index += 1;
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ring_buffer_index &= lzssRingBufferMask;
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} else {
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if (*length < 2) {
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return false;
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}
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unsigned char bytes[2];
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if (!lzss_read_decode_byte(stream, &bytes[0]) || !lzss_read_decode_byte(stream, &bytes[1])) {
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return false;
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}
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*length -= 2;
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low = bytes[0];
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high = bytes[1];
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dict_offset = low | ((high & 0xF0) << 4);
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chunk_length = (high & 0x0F) + lzssMatchLengthBias;
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for (index = 0; index < chunk_length; index++) {
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dict_index = (dict_offset + index) & lzssRingBufferMask;
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*(*dest) = ring_buffer[dict_index];
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ring_buffer[ring_buffer_index] = *(*dest)++;
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ring_buffer_index += 1;
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ring_buffer_index &= lzssRingBufferMask;
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}
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}
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return true;
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}
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} // namespace fallout
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