src/liblzma/delta/delta_encoder.c

   1 ///////////////////////////////////////////////////////////////////////////////
   2 //
   3 /// \file       delta_encoder.c
   4 /// \brief      Delta filter encoder
   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_encoder.h"
  14 #include "delta_private.h"
  15
  16
  17 /// Copies and encodes the data at the same time. This is used when Delta
  18 /// is the first filter in the chain (and thus the last filter in the
  19 /// encoder's filter stack).
  20 static void
  21 copy_and_encode(lzma_delta_coder *coder,
  22                 const uint8_t *restrict in, uint8_t *restrict out, size_t size)
  23 {
  24         const size_t distance = coder->distance;
  25
  26         for (size_t i = 0; i < size; ++i) {
  27                 const uint8_t tmp = coder->history[
  28                                 (distance + coder->pos) & 0xFF];
  29                 coder->history[coder->pos-- & 0xFF] = in[i];
  30                 out[i] = in[i] - tmp;
  31         }
  32 }
  33
  34
  35 /// Encodes the data in place. This is used when we are the last filter
  36 /// in the chain (and thus non-last filter in the encoder's filter stack).
  37 static void
  38 encode_in_place(lzma_delta_coder *coder, uint8_t *buffer, size_t size)
  39 {
  40         const size_t distance = coder->distance;
  41
  42         for (size_t i = 0; i < size; ++i) {
  43                 const uint8_t tmp = coder->history[
  44                                 (distance + coder->pos) & 0xFF];
  45                 coder->history[coder->pos-- & 0xFF] = buffer[i];
  46                 buffer[i] -= tmp;
  47         }
  48 }
  49
  50
  51 static lzma_ret
  52 delta_encode(void *coder_ptr, const lzma_allocator *allocator,
  53                 const uint8_t *restrict in, size_t *restrict in_pos,
  54                 size_t in_size, uint8_t *restrict out,
  55                 size_t *restrict out_pos, size_t out_size, lzma_action action)
  56 {
  57         lzma_delta_coder *coder = coder_ptr;
  58
  59         lzma_ret ret;
  60
  61         if (coder->next.code == NULL) {
  62                 const size_t in_avail = in_size - *in_pos;
  63                 const size_t out_avail = out_size - *out_pos;
  64                 const size_t size = my_min(in_avail, out_avail);
  65
  66                 // in and out might be NULL. In such cases size == 0.
  67                 // Null pointer + 0 is undefined behavior so skip
  68                 // the call in that case as it would do nothing anyway.
  69                 if (size > 0)
  70                         copy_and_encode(coder, in + *in_pos, out + *out_pos,
  71                                         size);
  72
  73                 *in_pos += size;
  74                 *out_pos += size;
  75
  76                 ret = action != LZMA_RUN && *in_pos == in_size
  77                                 ? LZMA_STREAM_END : LZMA_OK;
  78
  79         } else {
  80                 const size_t out_start = *out_pos;
  81
  82                 ret = coder->next.code(coder->next.coder, allocator,
  83                                 in, in_pos, in_size, out, out_pos, out_size,
  84                                 action);
  85
  86                 // Like above, avoid null pointer + 0.
  87                 const size_t size = *out_pos - out_start;
  88                 if (size > 0)
  89                         encode_in_place(coder, out + out_start, size);
  90         }
  91
  92         return ret;
  93 }
  94
  95
  96 static lzma_ret
  97 delta_encoder_update(void *coder_ptr, const lzma_allocator *allocator,
  98                 const lzma_filter *filters_null lzma_attribute((__unused__)),
  99                 const lzma_filter *reversed_filters)
 100 {
 101         lzma_delta_coder *coder = coder_ptr;
 102
 103         // Delta doesn't and will never support changing the options in
 104         // the middle of encoding. If the app tries to change them, we
 105         // simply ignore them.
 106         return lzma_next_filter_update(
 107                         &coder->next, allocator, reversed_filters + 1);
 108 }
 109
 110
 111 extern lzma_ret
 112 lzma_delta_encoder_init(lzma_next_coder *next, const lzma_allocator *allocator,
 113                 const lzma_filter_info *filters)
 114 {
 115         next->code = &delta_encode;
 116         next->update = &delta_encoder_update;
 117         return lzma_delta_coder_init(next, allocator, filters);
 118 }
 119
 120
 121 extern lzma_ret
 122 lzma_delta_props_encode(const void *options, uint8_t *out)
 123 {
 124         // The caller must have already validated the options, so it's
 125         // LZMA_PROG_ERROR if they are invalid.
 126         if (lzma_delta_coder_memusage(options) == UINT64_MAX)
 127                 return LZMA_PROG_ERROR;
 128
 129         const lzma_options_delta *opt = options;
 130         out[0] = opt->dist - LZMA_DELTA_DIST_MIN;
 131
 132         return LZMA_OK;
 133 }