src/liblzma/delta/delta_decoder.c

   1 ///////////////////////////////////////////////////////////////////////////////
   2 //
   3 /// \file       delta_decoder.c
   4 /// \brief      Delta filter decoder
   5 //
   6 //  Author:     Lasse Collin
   7 //
   8 //  This file has been put into the public domain.
   9 //  You can do whatever you want with this file.
  10 //
  11 ///////////////////////////////////////////////////////////////////////////////
  12
  13 #include "delta_decoder.h"
  14 #include "delta_private.h"
  15
  16
  17 static void
  18 decode_buffer(lzma_delta_coder *coder, uint8_t *buffer, size_t size)
  19 {
  20         const size_t distance = coder->distance;
  21
  22         for (size_t i = 0; i < size; ++i) {
  23                 buffer[i] += coder->history[(distance + coder->pos) & 0xFF];
  24                 coder->history[coder->pos-- & 0xFF] = buffer[i];
  25         }
  26 }
  27
  28
  29 static lzma_ret
  30 delta_decode(void *coder_ptr, const lzma_allocator *allocator,
  31                 const uint8_t *restrict in, size_t *restrict in_pos,
  32                 size_t in_size, uint8_t *restrict out,
  33                 size_t *restrict out_pos, size_t out_size, lzma_action action)
  34 {
  35         lzma_delta_coder *coder = coder_ptr;
  36
  37         assert(coder->next.code != NULL);
  38
  39         const size_t out_start = *out_pos;
  40
  41         const lzma_ret ret = coder->next.code(coder->next.coder, allocator,
  42                         in, in_pos, in_size, out, out_pos, out_size,
  43                         action);
  44
  45         // out might be NULL. In that case size == 0. Null pointer + 0 is
  46         // undefined behavior so skip the call in that case as it would
  47         // do nothing anyway.
  48         const size_t size = *out_pos - out_start;
  49         if (size > 0)
  50                 decode_buffer(coder, out + out_start, size);
  51
  52         return ret;
  53 }
  54
  55
  56 extern lzma_ret
  57 lzma_delta_decoder_init(lzma_next_coder *next, const lzma_allocator *allocator,
  58                 const lzma_filter_info *filters)
  59 {
  60         next->code = &delta_decode;
  61         return lzma_delta_coder_init(next, allocator, filters);
  62 }
  63
  64
  65 extern lzma_ret
  66 lzma_delta_props_decode(void **options, const lzma_allocator *allocator,
  67                 const uint8_t *props, size_t props_size)
  68 {
  69         if (props_size != 1)
  70                 return LZMA_OPTIONS_ERROR;
  71
  72         lzma_options_delta *opt
  73                         = lzma_alloc(sizeof(lzma_options_delta), allocator);
  74         if (opt == NULL)
  75                 return LZMA_MEM_ERROR;
  76
  77         opt->type = LZMA_DELTA_TYPE_BYTE;
  78         opt->dist = props[0] + 1U;
  79
  80         *options = opt;
  81
  82         return LZMA_OK;
  83 }