///////////////////////////////////////////////////////////////////////////////
//
/// \file delta_coder.c
/// \brief Encoder and decoder for the Delta filter
//
// Copyright (C) 2007 Lasse Collin
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// Lesser General Public License for more details.
//
///////////////////////////////////////////////////////////////////////////////
#include "delta_coder.h"
struct lzma_coder_s {
/// Next coder in the chain
lzma_next_coder next;
/// Uncompressed size - This is needed when we are the last
/// filter in the chain.
lzma_vli uncompressed_size;
/// Delta distance
size_t distance;
/// True if we are encoding; false if decoding
bool is_encoder;
/// Position in history[]
uint8_t pos;
/// Buffer to hold history of the original data
uint8_t history[LZMA_DELTA_DISTANCE_MAX];
};
static void
encode_buffer(lzma_coder *coder, uint8_t *buffer, size_t size)
{
const size_t distance = coder->distance;
for (size_t i = 0; i < size; ++i) {
const uint8_t tmp = coder->history[
(distance + coder->pos) & 0xFF];
coder->history[coder->pos--] = buffer[i];
buffer[i] -= tmp;
}
return;
}
static void
decode_buffer(lzma_coder *coder, uint8_t *buffer, size_t size)
{
const size_t distance = coder->distance;
for (size_t i = 0; i < size; ++i) {
buffer[i] += coder->history[(distance + coder->pos) & 0xFF];
coder->history[coder->pos--] = buffer[i];
}
return;
}
static lzma_ret
delta_code(lzma_coder *coder, lzma_allocator *allocator,
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)
{
const size_t out_start = *out_pos;
size_t size;
lzma_ret ret;
if (coder->next.code == NULL) {
if (!coder->is_encoder) {
// Limit in_size so that we don't copy too much.
if ((lzma_vli)(in_size - *in_pos)
> coder->uncompressed_size)
in_size = *in_pos + (size_t)(
coder->uncompressed_size);
}
size = bufcpy(in, in_pos, in_size, out, out_pos, out_size);
if (coder->uncompressed_size != LZMA_VLI_VALUE_UNKNOWN)
coder->uncompressed_size -= size;
// action can be LZMA_FINISH only in the encoder.
ret = (action == LZMA_FINISH && *in_pos == in_size)
|| coder->uncompressed_size == 0
? LZMA_STREAM_END : LZMA_OK;
} else {
ret = coder->next.code(coder->next.coder, allocator,
in, in_pos, in_size, out, out_pos, out_size,
action);
if (ret != LZMA_OK && ret != LZMA_STREAM_END)
return ret;
size = *out_pos - out_start;
}
if (coder->is_encoder)
encode_buffer(coder, out + out_start, size);
else
decode_buffer(coder, out + out_start, size);
return ret;
}
static void
delta_coder_end(lzma_coder *coder, lzma_allocator *allocator)
{
lzma_next_coder_end(&coder->next, allocator);
lzma_free(coder, allocator);
return;
}
static lzma_ret
delta_coder_init(lzma_next_coder *next, lzma_allocator *allocator,
const lzma_filter_info *filters, bool is_encoder)
{
// Allocate memory for the decoder if needed.
if (next->coder == NULL) {
next->coder = lzma_alloc(sizeof(lzma_coder), allocator);
if (next->coder == NULL)
return LZMA_MEM_ERROR;
next->code = &delta_code;
next->end = &delta_coder_end;
next->coder->next = LZMA_NEXT_CODER_INIT;
}
// Copy Uncompressed Size which is used to limit the output size.
next->coder->uncompressed_size = filters[0].uncompressed_size;
// The coder acts slightly differently as encoder and decoder.
next->coder->is_encoder = is_encoder;
// Set the delta distance.
if (filters[0].options == NULL)
return LZMA_PROG_ERROR;
next->coder->distance = ((lzma_options_delta *)(filters[0].options))
->distance;
if (next->coder->distance < LZMA_DELTA_DISTANCE_MIN
|| next->coder->distance > LZMA_DELTA_DISTANCE_MAX)
return LZMA_HEADER_ERROR;
// Initialize the rest of the variables.
next->coder->pos = 0;
memzero(next->coder->history, LZMA_DELTA_DISTANCE_MAX);
// Initialize the next decoder in the chain, if any.
return lzma_next_filter_init(&next->coder->next,
allocator, filters + 1);
}
#ifdef HAVE_ENCODER
extern lzma_ret
lzma_delta_encoder_init(lzma_next_coder *next, lzma_allocator *allocator,
const lzma_filter_info *filters)
{
return delta_coder_init(next, allocator, filters, true);
}
#endif
#ifdef HAVE_DECODER
extern lzma_ret
lzma_delta_decoder_init(lzma_next_coder *next, lzma_allocator *allocator,
const lzma_filter_info *filters)
{
return delta_coder_init(next, allocator, filters, false);
}
#endif
