external/public-domain/xz/dist/src/liblzma/simple/x86.c

   1 ///////////////////////////////////////////////////////////////////////////////
   2 //
   3 /// \file       x86.c
   4 /// \brief      Filter for x86 binaries (BCJ filter)
   5 ///
   6 //  Authors:    Igor Pavlov
   7 //              Lasse Collin
   8 //
   9 //  This file has been put into the public domain.
  10 //  You can do whatever you want with this file.
  11 //
  12 ///////////////////////////////////////////////////////////////////////////////
  13
  14 #include "simple_private.h"
  15
  16
  17 #define Test86MSByte(b) ((b) == 0 || (b) == 0xFF)
  18
  19
  20 struct lzma_simple_s {
  21         uint32_t prev_mask;
  22         uint32_t prev_pos;
  23 };
  24
  25
  26 static size_t
  27 x86_code(lzma_simple *simple, uint32_t now_pos, bool is_encoder,
  28                 uint8_t *buffer, size_t size)
  29 {
  30         static const bool MASK_TO_ALLOWED_STATUS[8]
  31                 = { true, true, true, false, true, false, false, false };
  32
  33         static const uint32_t MASK_TO_BIT_NUMBER[8]
  34                         = { 0, 1, 2, 2, 3, 3, 3, 3 };
  35
  36         uint32_t prev_mask = simple->prev_mask;
  37         uint32_t prev_pos = simple->prev_pos;
  38
  39         if (size < 5)
  40                 return 0;
  41
  42         if (now_pos - prev_pos > 5)
  43                 prev_pos = now_pos - 5;
  44
  45         const size_t limit = size - 5;
  46         size_t buffer_pos = 0;
  47
  48         while (buffer_pos <= limit) {
  49                 uint8_t b = buffer[buffer_pos];
  50                 if (b != 0xE8 && b != 0xE9) {
  51                         ++buffer_pos;
  52                         continue;
  53                 }
  54
  55                 const uint32_t offset = now_pos + (uint32_t)(buffer_pos)
  56                                 - prev_pos;
  57                 prev_pos = now_pos + (uint32_t)(buffer_pos);
  58
  59                 if (offset > 5) {
  60                         prev_mask = 0;
  61                 } else {
  62                         for (uint32_t i = 0; i < offset; ++i) {
  63                                 prev_mask &= 0x77;
  64                                 prev_mask <<= 1;
  65                         }
  66                 }
  67
  68                 b = buffer[buffer_pos + 4];
  69
  70                 if (Test86MSByte(b)
  71                         && MASK_TO_ALLOWED_STATUS[(prev_mask >> 1) & 0x7]
  72                                 && (prev_mask >> 1) < 0x10) {
  73
  74                         uint32_t src = ((uint32_t)(b) << 24)
  75                                 | ((uint32_t)(buffer[buffer_pos + 3]) << 16)
  76                                 | ((uint32_t)(buffer[buffer_pos + 2]) << 8)
  77                                 | (buffer[buffer_pos + 1]);
  78
  79                         uint32_t dest;
  80                         while (true) {
  81                                 if (is_encoder)
  82                                         dest = src + (now_pos + (uint32_t)(
  83                                                         buffer_pos) + 5);
  84                                 else
  85                                         dest = src - (now_pos + (uint32_t)(
  86                                                         buffer_pos) + 5);
  87
  88                                 if (prev_mask == 0)
  89                                         break;
  90
  91                                 const uint32_t i = MASK_TO_BIT_NUMBER[
  92                                                 prev_mask >> 1];
  93
  94                                 b = (uint8_t)(dest >> (24 - i * 8));
  95
  96                                 if (!Test86MSByte(b))
  97                                         break;
  98
  99                                 src = dest ^ ((1 << (32 - i * 8)) - 1);
 100                         }
 101
 102                         buffer[buffer_pos + 4]
 103                                         = (uint8_t)(~(((dest >> 24) & 1) - 1));
 104                         buffer[buffer_pos + 3] = (uint8_t)(dest >> 16);
 105                         buffer[buffer_pos + 2] = (uint8_t)(dest >> 8);
 106                         buffer[buffer_pos + 1] = (uint8_t)(dest);
 107                         buffer_pos += 5;
 108                         prev_mask = 0;
 109
 110                 } else {
 111                         ++buffer_pos;
 112                         prev_mask |= 1;
 113                         if (Test86MSByte(b))
 114                                 prev_mask |= 0x10;
 115                 }
 116         }
 117
 118         simple->prev_mask = prev_mask;
 119         simple->prev_pos = prev_pos;
 120
 121         return buffer_pos;
 122 }
 123
 124
 125 static lzma_ret
 126 x86_coder_init(lzma_next_coder *next, const lzma_allocator *allocator,
 127                 const lzma_filter_info *filters, bool is_encoder)
 128 {
 129         const lzma_ret ret = lzma_simple_coder_init(next, allocator, filters,
 130                         &x86_code, sizeof(lzma_simple), 5, 1, is_encoder);
 131
 132         if (ret == LZMA_OK) {
 133                 next->coder->simple->prev_mask = 0;
 134                 next->coder->simple->prev_pos = (uint32_t)(-5);
 135         }
 136
 137         return ret;
 138 }
 139
 140
 141 extern lzma_ret
 142 lzma_simple_x86_encoder_init(lzma_next_coder *next,
 143                 const lzma_allocator *allocator,
 144                 const lzma_filter_info *filters)
 145 {
 146         return x86_coder_init(next, allocator, filters, true);
 147 }
 148
 149
 150 extern lzma_ret
 151 lzma_simple_x86_decoder_init(lzma_next_coder *next,
 152                 const lzma_allocator *allocator,
 153                 const lzma_filter_info *filters)
 154 {
 155         return x86_coder_init(next, allocator, filters, false);
 156 }