src/liblzma/delta/delta_encoder.c

   1 // SPDX-License-Identifier: 0BSD
   2
   3 ///////////////////////////////////////////////////////////////////////////////
   4 //
   5 /// \file       delta_encoder.c
   6 /// \brief      Delta filter encoder
   7 //
   8 //  Author:     Lasse Collin
   9 //
  10 ///////////////////////////////////////////////////////////////////////////////
  11
  12 #include "delta_encoder.h"
  13 #include "delta_private.h"
  14
  15
  16 /// Copies and encodes the data at the same time. This is used when Delta
  17 /// is the first filter in the chain (and thus the last filter in the
  18 /// encoder's filter stack).
  19 static void
  20 copy_and_encode(lzma_delta_coder *coder,
  21                 const uint8_t *restrict in, uint8_t *restrict out, size_t size)
  22 {
  23         const size_t distance = coder->distance;
  24
  25         for (size_t i = 0; i < size; ++i) {
  26                 const uint8_t tmp = coder->history[
  27                                 (distance + coder->pos) & 0xFF];
  28                 coder->history[coder->pos-- & 0xFF] = in[i];
  29                 out[i] = in[i] - tmp;
  30         }
  31 }
  32
  33
  34 /// Encodes the data in place. This is used when we are the last filter
  35 /// in the chain (and thus non-last filter in the encoder's filter stack).
  36 static void
  37 encode_in_place(lzma_delta_coder *coder, uint8_t *buffer, size_t size)
  38 {
  39         const size_t distance = coder->distance;
  40
  41         for (size_t i = 0; i < size; ++i) {
  42                 const uint8_t tmp = coder->history[
  43                                 (distance + coder->pos) & 0xFF];
  44                 coder->history[coder->pos-- & 0xFF] = buffer[i];
  45                 buffer[i] -= tmp;
  46         }
  47 }
  48
  49
  50 static lzma_ret
  51 delta_encode(void *coder_ptr, const lzma_allocator *allocator,
  52                 const uint8_t *restrict in, size_t *restrict in_pos,
  53                 size_t in_size, uint8_t *restrict out,
  54                 size_t *restrict out_pos, size_t out_size, lzma_action action)
  55 {
  56         lzma_delta_coder *coder = coder_ptr;
  57
  58         lzma_ret ret;
  59
  60         if (coder->next.code == NULL) {
  61                 const size_t in_avail = in_size - *in_pos;
  62                 const size_t out_avail = out_size - *out_pos;
  63                 const size_t size = my_min(in_avail, out_avail);
  64
  65                 // in and out might be NULL. In such cases size == 0.
  66                 // Null pointer + 0 is undefined behavior so skip
  67                 // the call in that case as it would do nothing anyway.
  68                 if (size > 0)
  69                         copy_and_encode(coder, in + *in_pos, out + *out_pos,
  70                                         size);
  71
  72                 *in_pos += size;
  73                 *out_pos += size;
  74
  75                 ret = action != LZMA_RUN && *in_pos == in_size
  76                                 ? LZMA_STREAM_END : LZMA_OK;
  77
  78         } else {
  79                 const size_t out_start = *out_pos;
  80
  81                 ret = coder->next.code(coder->next.coder, allocator,
  82                                 in, in_pos, in_size, out, out_pos, out_size,
  83                                 action);
  84
  85                 // Like above, avoid null pointer + 0.
  86                 const size_t size = *out_pos - out_start;
  87                 if (size > 0)
  88                         encode_in_place(coder, out + out_start, size);
  89         }
  90
  91         return ret;
  92 }
  93
  94
  95 static lzma_ret
  96 delta_encoder_update(void *coder_ptr, const lzma_allocator *allocator,
  97                 const lzma_filter *filters_null lzma_attribute((__unused__)),
  98                 const lzma_filter *reversed_filters)
  99 {
 100         lzma_delta_coder *coder = coder_ptr;
 101
 102         // Delta doesn't and will never support changing the options in
 103         // the middle of encoding. If the app tries to change them, we
 104         // simply ignore them.
 105         return lzma_next_filter_update(
 106                         &coder->next, allocator, reversed_filters + 1);
 107 }
 108
 109
 110 extern lzma_ret
 111 lzma_delta_encoder_init(lzma_next_coder *next, const lzma_allocator *allocator,
 112                 const lzma_filter_info *filters)
 113 {
 114         next->code = &delta_encode;
 115         next->update = &delta_encoder_update;
 116         return lzma_delta_coder_init(next, allocator, filters);
 117 }
 118
 119
 120 extern lzma_ret
 121 lzma_delta_props_encode(const void *options, uint8_t *out)
 122 {
 123         // The caller must have already validated the options, so it's
 124         // LZMA_PROG_ERROR if they are invalid.
 125         if (lzma_delta_coder_memusage(options) == UINT64_MAX)
 126                 return LZMA_PROG_ERROR;
 127
 128         const lzma_options_delta *opt = options;
 129         out[0] = opt->dist - LZMA_DELTA_DIST_MIN;
 130
 131         return LZMA_OK;
 132 }