src/liblzma/common/delta_coder.c

   1 ///////////////////////////////////////////////////////////////////////////////
   2 //
   3 /// \file       delta_coder.c
   4 /// \brief      Encoder and decoder for the Delta filter
   5 //
   6 //  Copyright (C) 2007 Lasse Collin
   7 //
   8 //  This library is free software; you can redistribute it and/or
   9 //  modify it under the terms of the GNU Lesser General Public
  10 //  License as published by the Free Software Foundation; either
  11 //  version 2.1 of the License, or (at your option) any later version.
  12 //
  13 //  This library is distributed in the hope that it will be useful,
  14 //  but WITHOUT ANY WARRANTY; without even the implied warranty of
  15 //  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  16 //  Lesser General Public License for more details.
  17 //
  18 ///////////////////////////////////////////////////////////////////////////////
  19
  20 #include "delta_coder.h"
  21
  22
  23 struct lzma_coder_s {
  24         /// Next coder in the chain
  25         lzma_next_coder next;
  26
  27         /// Uncompressed size - This is needed when we are the last
  28         /// filter in the chain.
  29         lzma_vli uncompressed_size;
  30
  31         /// Delta distance
  32         size_t distance;
  33
  34         /// True if we are encoding; false if decoding
  35         bool is_encoder;
  36
  37         /// Position in history[]
  38         uint8_t pos;
  39
  40         /// Buffer to hold history of the original data
  41         uint8_t history[LZMA_DELTA_DISTANCE_MAX];
  42 };
  43
  44
  45 static void
  46 encode_buffer(lzma_coder *coder, uint8_t *buffer, size_t size)
  47 {
  48         const size_t distance = coder->distance;
  49
  50         for (size_t i = 0; i < size; ++i) {
  51                 const uint8_t tmp = coder->history[
  52                                 (distance + coder->pos) & 0xFF];
  53                 coder->history[coder->pos--] = buffer[i];
  54                 buffer[i] -= tmp;
  55         }
  56
  57         return;
  58 }
  59
  60
  61 static void
  62 decode_buffer(lzma_coder *coder, uint8_t *buffer, size_t size)
  63 {
  64         const size_t distance = coder->distance;
  65
  66         for (size_t i = 0; i < size; ++i) {
  67                 buffer[i] += coder->history[(distance + coder->pos) & 0xFF];
  68                 coder->history[coder->pos--] = buffer[i];
  69         }
  70
  71         return;
  72 }
  73
  74
  75 static lzma_ret
  76 delta_code(lzma_coder *coder, lzma_allocator *allocator,
  77                 const uint8_t *restrict in, size_t *restrict in_pos,
  78                 size_t in_size, uint8_t *restrict out,
  79                 size_t *restrict out_pos, size_t out_size, lzma_action action)
  80 {
  81         const size_t out_start = *out_pos;
  82         size_t size;
  83         lzma_ret ret;
  84
  85         if (coder->next.code == NULL) {
  86                 if (!coder->is_encoder) {
  87                         // Limit in_size so that we don't copy too much.
  88                         if ((lzma_vli)(in_size - *in_pos)
  89                                         > coder->uncompressed_size)
  90                                 in_size = *in_pos + (size_t)(
  91                                                 coder->uncompressed_size);
  92                 }
  93
  94                 size = bufcpy(in, in_pos, in_size, out, out_pos, out_size);
  95
  96                 if (coder->uncompressed_size != LZMA_VLI_VALUE_UNKNOWN)
  97                         coder->uncompressed_size -= size;
  98
  99                 // action can be LZMA_FINISH only in the encoder.
 100                 ret = (action == LZMA_FINISH && *in_pos == in_size)
 101                                         || coder->uncompressed_size == 0
 102                                 ? LZMA_STREAM_END : LZMA_OK;
 103
 104         } else {
 105                 ret = coder->next.code(coder->next.coder, allocator,
 106                                 in, in_pos, in_size, out, out_pos, out_size,
 107                                 action);
 108                 if (ret != LZMA_OK && ret != LZMA_STREAM_END)
 109                         return ret;
 110
 111                 size = *out_pos - out_start;
 112         }
 113
 114         if (coder->is_encoder)
 115                 encode_buffer(coder, out + out_start, size);
 116         else
 117                 decode_buffer(coder, out + out_start, size);
 118
 119         return ret;
 120 }
 121
 122
 123 static void
 124 delta_coder_end(lzma_coder *coder, lzma_allocator *allocator)
 125 {
 126         lzma_next_coder_end(&coder->next, allocator);
 127         lzma_free(coder, allocator);
 128         return;
 129 }
 130
 131
 132 static lzma_ret
 133 delta_coder_init(lzma_next_coder *next, lzma_allocator *allocator,
 134                 const lzma_filter_info *filters, bool is_encoder)
 135 {
 136         // Allocate memory for the decoder if needed.
 137         if (next->coder == NULL) {
 138                 next->coder = lzma_alloc(sizeof(lzma_coder), allocator);
 139                 if (next->coder == NULL)
 140                         return LZMA_MEM_ERROR;
 141
 142                 next->code = &delta_code;
 143                 next->end = &delta_coder_end;
 144                 next->coder->next = LZMA_NEXT_CODER_INIT;
 145         }
 146
 147         // Copy Uncompressed Size which is used to limit the output size.
 148         next->coder->uncompressed_size = filters[0].uncompressed_size;
 149
 150         // The coder acts slightly differently as encoder and decoder.
 151         next->coder->is_encoder = is_encoder;
 152
 153         // Set the delta distance.
 154         if (filters[0].options == NULL)
 155                 return LZMA_PROG_ERROR;
 156         next->coder->distance = ((lzma_options_delta *)(filters[0].options))
 157                         ->distance;
 158         if (next->coder->distance < LZMA_DELTA_DISTANCE_MIN
 159                         || next->coder->distance > LZMA_DELTA_DISTANCE_MAX)
 160                 return LZMA_HEADER_ERROR;
 161
 162         // Initialize the rest of the variables.
 163         next->coder->pos = 0;
 164         memzero(next->coder->history, LZMA_DELTA_DISTANCE_MAX);
 165
 166         // Initialize the next decoder in the chain, if any.
 167         return lzma_next_filter_init(&next->coder->next,
 168                                 allocator, filters + 1);
 169 }
 170
 171
 172 #ifdef HAVE_ENCODER
 173 extern lzma_ret
 174 lzma_delta_encoder_init(lzma_next_coder *next, lzma_allocator *allocator,
 175                 const lzma_filter_info *filters)
 176 {
 177         return delta_coder_init(next, allocator, filters, true);
 178 }
 179 #endif
 180
 181
 182 #ifdef HAVE_DECODER
 183 extern lzma_ret
 184 lzma_delta_decoder_init(lzma_next_coder *next, lzma_allocator *allocator,
 185                 const lzma_filter_info *filters)
 186 {
 187         return delta_coder_init(next, allocator, filters, false);
 188 }
 189 #endif