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/// \file lz_decoder.c
/// \brief LZ out window
// Authors: Igor Pavlov
// Lasse Collin
// This file has been put into the public domain.
// You can do whatever you want with this file.
// liblzma supports multiple LZ77-based filters. The LZ part is shared
// between these filters. The LZ code takes care of dictionary handling
// and passing the data between filters in the chain. The filter-specific
// part decodes from the input buffer to the dictionary.
#include "lz_decoder.h"
typedef struct {
/// Dictionary (history buffer)
lzma_dict dict;
/// The actual LZ-based decoder e.g. LZMA
lzma_lz_decoder lz;
/// Next filter in the chain, if any. Note that LZMA and LZMA2 are
/// only allowed as the last filter, but the long-range filter in
/// future can be in the middle of the chain.
lzma_next_coder next;
/// True if the next filter in the chain has returned LZMA_STREAM_END.
bool next_finished;
/// True if the LZ decoder (e.g. LZMA) has detected end of payload
/// marker. This may become true before next_finished becomes true.
bool this_finished;
/// Temporary buffer needed when the LZ-based filter is not the last
/// filter in the chain. The output of the next filter is first
/// decoded into buffer[], which is then used as input for the actual
/// LZ-based decoder.
struct {
size_t pos;
size_t size;
uint8_t buffer[LZMA_BUFFER_SIZE];
} temp;
} lzma_coder;
static void
lz_decoder_reset(lzma_coder *coder)
coder->dict.pos = 0;
coder->dict.full = 0;
coder->dict.buf[coder->dict.size - 1] = '\0';
coder->dict.need_reset = false;
static lzma_ret
decode_buffer(lzma_coder *coder,
const uint8_t *restrict in, size_t *restrict in_pos,
size_t in_size, uint8_t *restrict out,
size_t *restrict out_pos, size_t out_size)
while (true) {
// Wrap the dictionary if needed.
if (coder->dict.pos == coder->dict.size)
coder->dict.pos = 0;
// Store the current dictionary position. It is needed to know
// where to start copying to the out[] buffer.
const size_t dict_start = coder->dict.pos;
// Calculate how much we allow coder->lz.code() to decode.
// It must not decode past the end of the dictionary
// buffer, and we don't want it to decode more than is
// actually needed to fill the out[] buffer.
coder->dict.limit = coder->dict.pos
+ my_min(out_size - *out_pos,
coder->dict.size - coder->dict.pos);
// Call the coder->lz.code() to do the actual decoding.
const lzma_ret ret = coder->lz.code(
coder->lz.coder, &coder->dict,
in, in_pos, in_size);
// Copy the decoded data from the dictionary to the out[]
// buffer.
const size_t copy_size = coder->dict.pos - dict_start;
assert(copy_size <= out_size - *out_pos);
memcpy(out + *out_pos, coder->dict.buf + dict_start,
*out_pos += copy_size;
// Reset the dictionary if so requested by coder->lz.code().
if (coder->dict.need_reset) {
// Since we reset dictionary, we don't check if
// dictionary became full.
if (ret != LZMA_OK || *out_pos == out_size)
return ret;
} else {
// Return if everything got decoded or an error
// occurred, or if there's no more data to decode.
// Note that detecting if there's something to decode
// is done by looking if dictionary become full
// instead of looking if *in_pos == in_size. This
// is because it is possible that all the input was
// consumed already but some data is pending to be
// written to the dictionary.
if (ret != LZMA_OK || *out_pos == out_size
|| coder->dict.pos < coder->dict.size)
return ret;
static lzma_ret
lz_decode(void *coder_ptr,
const lzma_allocator *allocator lzma_attribute((__unused__)),
const uint8_t *restrict in, size_t *restrict in_pos,
size_t in_size, uint8_t *restrict out,
size_t *restrict out_pos, size_t out_size,
lzma_action action)
lzma_coder *coder = coder_ptr;
if (coder->next.code == NULL)
return decode_buffer(coder, in, in_pos, in_size,
out, out_pos, out_size);
// We aren't the last coder in the chain, we need to decode
// our input to a temporary buffer.
while (*out_pos < out_size) {
// Fill the temporary buffer if it is empty.
if (!coder->next_finished
&& coder->temp.pos == coder->temp.size) {
coder->temp.pos = 0;
coder->temp.size = 0;
const lzma_ret ret = coder->next.code(
allocator, in, in_pos, in_size,
coder->temp.buffer, &coder->temp.size,
if (ret == LZMA_STREAM_END)
coder->next_finished = true;
else if (ret != LZMA_OK || coder->temp.size == 0)
return ret;
if (coder->this_finished) {
if (coder->temp.size != 0)
if (coder->next_finished)
return LZMA_OK;
const lzma_ret ret = decode_buffer(coder, coder->temp.buffer,
&coder->temp.pos, coder->temp.size,
out, out_pos, out_size);
if (ret == LZMA_STREAM_END)
coder->this_finished = true;
else if (ret != LZMA_OK)
return ret;
else if (coder->next_finished && *out_pos < out_size)
return LZMA_OK;
static void
lz_decoder_end(void *coder_ptr, const lzma_allocator *allocator)
lzma_coder *coder = coder_ptr;
lzma_next_end(&coder->next, allocator);
lzma_free(coder->dict.buf, allocator);
if (coder->lz.end != NULL)
coder->lz.end(coder->lz.coder, allocator);
lzma_free(coder->lz.coder, allocator);
lzma_free(coder, allocator);
extern lzma_ret
lzma_lz_decoder_init(lzma_next_coder *next, const lzma_allocator *allocator,
const lzma_filter_info *filters,
lzma_ret (*lz_init)(lzma_lz_decoder *lz,
const lzma_allocator *allocator, const void *options,
lzma_lz_options *lz_options))
// Allocate the base structure if it isn't already allocated.
lzma_coder *coder = next->coder;
if (coder == NULL) {
coder = lzma_alloc(sizeof(lzma_coder), allocator);
if (coder == NULL)
next->coder = coder;
next->code = &lz_decode;
next->end = &lz_decoder_end;
coder->dict.buf = NULL;
coder->dict.size = 0;
coder->next = LZMA_NEXT_CODER_INIT;
// Allocate and initialize the LZ-based decoder. It will also give
// us the dictionary size.
lzma_lz_options lz_options;
return_if_error(lz_init(&coder->lz, allocator,
filters[0].options, &lz_options));
// If the dictionary size is very small, increase it to 4096 bytes.
// This is to prevent constant wrapping of the dictionary, which
// would slow things down. The downside is that since we don't check
// separately for the real dictionary size, we may happily accept
// corrupt files.
if (lz_options.dict_size < 4096)
lz_options.dict_size = 4096;
// Make dictionary size a multipe of 16. Some LZ-based decoders like
// LZMA use the lowest bits lzma_dict.pos to know the alignment of the
// data. Aligned buffer is also good when memcpying from the
// dictionary to the output buffer, since applications are
// recommended to give aligned buffers to liblzma.
// Avoid integer overflow.
if (lz_options.dict_size > SIZE_MAX - 15)
lz_options.dict_size = (lz_options.dict_size + 15) & ~((size_t)(15));
// Allocate and initialize the dictionary.
if (coder->dict.size != lz_options.dict_size) {
lzma_free(coder->dict.buf, allocator);
= lzma_alloc(lz_options.dict_size, allocator);
if (coder->dict.buf == NULL)
coder->dict.size = lz_options.dict_size;
// Use the preset dictionary if it was given to us.
if (lz_options.preset_dict != NULL
&& lz_options.preset_dict_size > 0) {
// If the preset dictionary is bigger than the actual
// dictionary, copy only the tail.
const size_t copy_size = my_min(lz_options.preset_dict_size,
const size_t offset = lz_options.preset_dict_size - copy_size;
memcpy(coder->dict.buf, lz_options.preset_dict + offset,
coder->dict.pos = copy_size;
coder->dict.full = copy_size;
// Miscellaneous initializations
coder->next_finished = false;
coder->this_finished = false;
coder->temp.pos = 0;
coder->temp.size = 0;
// Initialize the next filter in the chain, if any.
return lzma_next_filter_init(&coder->next, allocator, filters + 1);
extern uint64_t
lzma_lz_decoder_memusage(size_t dictionary_size)
return sizeof(lzma_coder) + (uint64_t)(dictionary_size);
extern void
lzma_lz_decoder_uncompressed(void *coder_ptr, lzma_vli uncompressed_size)
lzma_coder *coder = coder_ptr;
coder->lz.set_uncompressed(coder->lz.coder, uncompressed_size);