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                         uint32_t i;
  63                         for (i = 0; i < offset; ++i) {
  64                                 prev_mask &= 0x77;
  65                                 prev_mask <<= 1;
  66                         }
  67                 }
  68
  69                 b = buffer[buffer_pos + 4];
  70
  71                 if (Test86MSByte(b)
  72                         && MASK_TO_ALLOWED_STATUS[(prev_mask >> 1) & 0x7]
  73                                 && (prev_mask >> 1) < 0x10) {
  74
  75                         uint32_t src = ((uint32_t)(b) << 24)
  76                                 | ((uint32_t)(buffer[buffer_pos + 3]) << 16)
  77                                 | ((uint32_t)(buffer[buffer_pos + 2]) << 8)
  78                                 | (buffer[buffer_pos + 1]);
  79
  80                         uint32_t dest;
  81                         while (true) {
  82                                 if (is_encoder)
  83                                         dest = src + (now_pos + (uint32_t)(
  84                                                         buffer_pos) + 5);
  85                                 else
  86                                         dest = src - (now_pos + (uint32_t)(
  87                                                         buffer_pos) + 5);
  88
  89                                 if (prev_mask == 0)
  90                                         break;
  91
  92                                 const uint32_t i = MASK_TO_BIT_NUMBER[
  93                                                 prev_mask >> 1];
  94
  95                                 b = (uint8_t)(dest >> (24 - i * 8));
  96
  97                                 if (!Test86MSByte(b))
  98                                         break;
  99
 100                                 src = dest ^ ((1 << (32 - i * 8)) - 1);
 101                         }
 102
 103                         buffer[buffer_pos + 4]
 104                                         = (uint8_t)(~(((dest >> 24) & 1) - 1));
 105                         buffer[buffer_pos + 3] = (uint8_t)(dest >> 16);
 106                         buffer[buffer_pos + 2] = (uint8_t)(dest >> 8);
 107                         buffer[buffer_pos + 1] = (uint8_t)(dest);
 108                         buffer_pos += 5;
 109                         prev_mask = 0;
 110
 111                 } else {
 112                         ++buffer_pos;
 113                         prev_mask |= 1;
 114                         if (Test86MSByte(b))
 115                                 prev_mask |= 0x10;
 116                 }
 117         }
 118
 119         simple->prev_mask = prev_mask;
 120         simple->prev_pos = prev_pos;
 121
 122         return buffer_pos;
 123 }
 124
 125
 126 static lzma_ret
 127 x86_coder_init(lzma_next_coder *next, lzma_allocator *allocator,
 128                 const lzma_filter_info *filters, bool is_encoder)
 129 {
 130         const lzma_ret ret = lzma_simple_coder_init(next, allocator, filters,
 131                         &x86_code, sizeof(lzma_simple), 5, 1, is_encoder);
 132
 133         if (ret == LZMA_OK) {
 134                 next->coder->simple->prev_mask = 0;
 135                 next->coder->simple->prev_pos = (uint32_t)(-5);
 136         }
 137
 138         return ret;
 139 }
 140
 141
 142 extern lzma_ret
 143 lzma_simple_x86_encoder_init(lzma_next_coder *next, 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, lzma_allocator *allocator,
 152                 const lzma_filter_info *filters)
 153 {
 154         return x86_coder_init(next, allocator, filters, false);
 155 }