external/public-domain/xz/dist/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_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_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(lzma_coder *coder, 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_ret ret;
  58
  59         if (coder->next.code == NULL) {
  60                 const size_t in_avail = in_size - *in_pos;
  61                 const size_t out_avail = out_size - *out_pos;
  62                 const size_t size = my_min(in_avail, out_avail);
  63
  64                 copy_and_encode(coder, in + *in_pos, out + *out_pos, size);
  65
  66                 *in_pos += size;
  67                 *out_pos += size;
  68
  69                 ret = action != LZMA_RUN && *in_pos == in_size
  70                                 ? LZMA_STREAM_END : LZMA_OK;
  71
  72         } else {
  73                 const size_t out_start = *out_pos;
  74
  75                 ret = coder->next.code(coder->next.coder, allocator,
  76                                 in, in_pos, in_size, out, out_pos, out_size,
  77                                 action);
  78
  79                 encode_in_place(coder, out + out_start, *out_pos - out_start);
  80         }
  81
  82         return ret;
  83 }
  84
  85
  86 static lzma_ret
  87 delta_encoder_update(lzma_coder *coder, const lzma_allocator *allocator,
  88                 const lzma_filter *filters_null lzma_attribute((__unused__)),
  89                 const lzma_filter *reversed_filters)
  90 {
  91         // Delta doesn't and will never support changing the options in
  92         // the middle of encoding. If the app tries to change them, we
  93         // simply ignore them.
  94         return lzma_next_filter_update(
  95                         &coder->next, allocator, reversed_filters + 1);
  96 }
  97
  98
  99 extern lzma_ret
 100 lzma_delta_encoder_init(lzma_next_coder *next, const lzma_allocator *allocator,
 101                 const lzma_filter_info *filters)
 102 {
 103         next->code = &delta_encode;
 104         next->update = &delta_encoder_update;
 105         return lzma_delta_coder_init(next, allocator, filters);
 106 }
 107
 108
 109 extern lzma_ret
 110 lzma_delta_props_encode(const void *options, uint8_t *out)
 111 {
 112         // The caller must have already validated the options, so it's
 113         // LZMA_PROG_ERROR if they are invalid.
 114         if (lzma_delta_coder_memusage(options) == UINT64_MAX)
 115                 return LZMA_PROG_ERROR;
 116
 117         const lzma_options_delta *opt = options;
 118         out[0] = opt->dist - LZMA_DELTA_DIST_MIN;
 119
 120         return LZMA_OK;
 121 }