Bra86.c revision baa3858d3f5d128a5c8466b700098109edcad5f2 
1/* Bra86.c -- Converter for x86 code (BCJ)
22008-10-04 : Igor Pavlov : Public domain */
3
4#include "Bra.h"
5
6#define Test86MSByte(b) ((b) == 0 || (b) == 0xFF)
7
8const Byte kMaskToAllowedStatus[8] = {1, 1, 1, 0, 1, 0, 0, 0};
9const Byte kMaskToBitNumber[8] = {0, 1, 2, 2, 3, 3, 3, 3};
10
11SizeT x86_Convert(Byte *data, SizeT size, UInt32 ip, UInt32 *state, int encoding)
12{
13  SizeT bufferPos = 0, prevPosT;
14  UInt32 prevMask = *state & 0x7;
15  if (size < 5)
16    return 0;
17  ip += 5;
18  prevPosT = (SizeT)0 - 1;
19
20  for (;;)
21  {
22    Byte *p = data + bufferPos;
23    Byte *limit = data + size - 4;
24    for (; p < limit; p++)
25      if ((*p & 0xFE) == 0xE8)
26        break;
27    bufferPos = (SizeT)(p - data);
28    if (p >= limit)
29      break;
30    prevPosT = bufferPos - prevPosT;
31    if (prevPosT > 3)
32      prevMask = 0;
33    else
34    {
35      prevMask = (prevMask << ((int)prevPosT - 1)) & 0x7;
36      if (prevMask != 0)
37      {
38        Byte b = p[4 - kMaskToBitNumber[prevMask]];
39        if (!kMaskToAllowedStatus[prevMask] || Test86MSByte(b))
40        {
41          prevPosT = bufferPos;
42          prevMask = ((prevMask << 1) & 0x7) | 1;
43          bufferPos++;
44          continue;
45        }
46      }
47    }
48    prevPosT = bufferPos;
49
50    if (Test86MSByte(p[4]))
51    {
52      UInt32 src = ((UInt32)p[4] << 24) | ((UInt32)p[3] << 16) | ((UInt32)p[2] << 8) | ((UInt32)p[1]);
53      UInt32 dest;
54      for (;;)
55      {
56        Byte b;
57        int index;
58        if (encoding)
59          dest = (ip + (UInt32)bufferPos) + src;
60        else
61          dest = src - (ip + (UInt32)bufferPos);
62        if (prevMask == 0)
63          break;
64        index = kMaskToBitNumber[prevMask] * 8;
65        b = (Byte)(dest >> (24 - index));
66        if (!Test86MSByte(b))
67          break;
68        src = dest ^ ((1 << (32 - index)) - 1);
69      }
70      p[4] = (Byte)(~(((dest >> 24) & 1) - 1));
71      p[3] = (Byte)(dest >> 16);
72      p[2] = (Byte)(dest >> 8);
73      p[1] = (Byte)dest;
74      bufferPos += 5;
75    }
76    else
77    {
78      prevMask = ((prevMask << 1) & 0x7) | 1;
79      bufferPos++;
80    }
81  }
82  prevPosT = bufferPos - prevPosT;
83  *state = ((prevPosT > 3) ? 0 : ((prevMask << ((int)prevPosT - 1)) & 0x7));
84  return bufferPos;
85}
86