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      1 /* Bra86.c -- Converter for x86 code (BCJ)
      2 2008-10-04 : Igor Pavlov : Public domain */
      3 
      4 #include "Bra.h"
      5 
      6 #define Test86MSByte(b) ((b) == 0 || (b) == 0xFF)
      7 
      8 const Byte kMaskToAllowedStatus[8] = {1, 1, 1, 0, 1, 0, 0, 0};
      9 const Byte kMaskToBitNumber[8] = {0, 1, 2, 2, 3, 3, 3, 3};
     10 
     11 SizeT 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