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///////////////////////////////////////////////////////////////////////////////
//
/// \file delta_encoder.c
/// \brief Delta filter encoder
//
// Author: Lasse Collin
//
// This file has been put into the public domain.
// You can do whatever you want with this file.
//
///////////////////////////////////////////////////////////////////////////////
#include "delta_encoder.h"
#include "delta_private.h"
/// Copies and encodes the data at the same time. This is used when Delta
/// is the first filter in the chain (and thus the last filter in the
/// encoder's filter stack).
static void
copy_and_encode(lzma_delta_coder *coder,
const uint8_t *restrict in, uint8_t *restrict out, 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-- & 0xFF] = in[i];
out[i] = in[i] - tmp;
}
}
/// Encodes the data in place. This is used when we are the last filter
/// in the chain (and thus non-last filter in the encoder's filter stack).
static void
encode_in_place(lzma_delta_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-- & 0xFF] = buffer[i];
buffer[i] -= tmp;
}
}
static lzma_ret
delta_encode(void *coder_ptr, const 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)
{
lzma_delta_coder *coder = coder_ptr;
lzma_ret ret;
if (coder->next.code == NULL) {
const size_t in_avail = in_size - *in_pos;
const size_t out_avail = out_size - *out_pos;
const size_t size = my_min(in_avail, out_avail);
// in and out might be NULL. In such cases size == 0.
// Null pointer + 0 is undefined behavior so skip
// the call in that case as it would do nothing anyway.
if (size > 0)
copy_and_encode(coder, in + *in_pos, out + *out_pos,
size);
*in_pos += size;
*out_pos += size;
ret = action != LZMA_RUN && *in_pos == in_size
? LZMA_STREAM_END : LZMA_OK;
} else {
const size_t out_start = *out_pos;
ret = coder->next.code(coder->next.coder, allocator,
in, in_pos, in_size, out, out_pos, out_size,
action);
// Like above, avoid null pointer + 0.
const size_t size = *out_pos - out_start;
if (size > 0)
encode_in_place(coder, out + out_start, size);
}
return ret;
}
static lzma_ret
delta_encoder_update(void *coder_ptr, const lzma_allocator *allocator,
const lzma_filter *filters_null lzma_attribute((__unused__)),
const lzma_filter *reversed_filters)
{
lzma_delta_coder *coder = coder_ptr;
// Delta doesn't and will never support changing the options in
// the middle of encoding. If the app tries to change them, we
// simply ignore them.
return lzma_next_filter_update(
&coder->next, allocator, reversed_filters + 1);
}
extern lzma_ret
lzma_delta_encoder_init(lzma_next_coder *next, const lzma_allocator *allocator,
const lzma_filter_info *filters)
{
next->code = &delta_encode;
next->update = &delta_encoder_update;
return lzma_delta_coder_init(next, allocator, filters);
}
extern lzma_ret
lzma_delta_props_encode(const void *options, uint8_t *out)
{
// The caller must have already validated the options, so it's
// LZMA_PROG_ERROR if they are invalid.
if (lzma_delta_coder_memusage(options) == UINT64_MAX)
return LZMA_PROG_ERROR;
const lzma_options_delta *opt = options;
out[0] = opt->dist - LZMA_DELTA_DIST_MIN;
return LZMA_OK;
}
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