mirror of https://git.tukaani.org/xz.git
120 lines
3.3 KiB
C
120 lines
3.3 KiB
C
///////////////////////////////////////////////////////////////////////////////
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//
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/// \file delta_encoder.c
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/// \brief Delta filter encoder
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//
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// Copyright (C) 2007, 2008 Lasse Collin
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//
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// This library is free software; you can redistribute it and/or
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// modify it under the terms of the GNU Lesser General Public
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// License as published by the Free Software Foundation; either
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// version 2.1 of the License, or (at your option) any later version.
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//
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// This library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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// Lesser General Public License for more details.
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//
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///////////////////////////////////////////////////////////////////////////////
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#include "delta_encoder.h"
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#include "delta_common.h"
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/// Copies and encodes the data at the same time. This is used when Delta
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/// is the first filter in the chain (and thus the last filter in the
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/// encoder's filter stack).
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static void
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copy_and_encode(lzma_coder *coder,
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const uint8_t *restrict in, uint8_t *restrict out, size_t size)
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{
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const size_t distance = coder->distance;
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for (size_t i = 0; i < size; ++i) {
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const uint8_t tmp = coder->history[
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(distance + coder->pos) & 0xFF];
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coder->history[coder->pos-- & 0xFF] = in[i];
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out[i] = in[i] - tmp;
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}
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}
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/// Encodes the data in place. This is used when we are the last filter
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/// in the chain (and thus non-last filter in the encoder's filter stack).
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static void
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encode_in_place(lzma_coder *coder, uint8_t *buffer, size_t size)
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{
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const size_t distance = coder->distance;
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for (size_t i = 0; i < size; ++i) {
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const uint8_t tmp = coder->history[
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(distance + coder->pos) & 0xFF];
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coder->history[coder->pos-- & 0xFF] = buffer[i];
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buffer[i] -= tmp;
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}
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}
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static lzma_ret
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delta_encode(lzma_coder *coder, lzma_allocator *allocator,
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const uint8_t *restrict in, size_t *restrict in_pos,
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size_t in_size, uint8_t *restrict out,
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size_t *restrict out_pos, size_t out_size, lzma_action action)
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{
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lzma_ret ret;
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if (coder->next.code == NULL) {
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const size_t in_avail = in_size - *in_pos;
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const size_t out_avail = out_size - *out_pos;
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const size_t size = MIN(in_avail, out_avail);
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copy_and_encode(coder, in + *in_pos, out + *out_pos, size);
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*in_pos += size;
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*out_pos += size;
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ret = action != LZMA_RUN && *in_pos == in_size
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? LZMA_STREAM_END : LZMA_OK;
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} else {
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const size_t out_start = *out_pos;
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ret = coder->next.code(coder->next.coder, allocator,
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in, in_pos, in_size, out, out_pos, out_size,
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action);
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encode_in_place(coder, out + out_start, *out_pos - out_start);
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}
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return ret;
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}
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extern lzma_ret
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lzma_delta_encoder_init(lzma_next_coder *next, lzma_allocator *allocator,
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const lzma_filter_info *filters)
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{
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return lzma_delta_coder_init(next, allocator, filters, &delta_encode);
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}
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extern lzma_ret
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lzma_delta_props_encode(const void *options, uint8_t *out)
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{
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if (options == NULL)
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return LZMA_PROG_ERROR;
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const lzma_options_delta *opt = options;
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// It's possible that newer liblzma versions will support larger
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// distance values.
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if (opt->type != LZMA_DELTA_TYPE_BYTE
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|| opt->distance < LZMA_DELTA_DISTANCE_MIN
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|| opt->distance > LZMA_DELTA_DISTANCE_MAX)
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return LZMA_OPTIONS_ERROR;
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out[0] = opt->distance - LZMA_DELTA_DISTANCE_MIN;
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return LZMA_OK;
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}
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