/* Bra86.c -- Converter for x86 code (BCJ)
 2008-10-04 : Igor Pavlov : Public domain */
 
 #include "Bra.h"
 
 #define Test86MSByte(b) ((b) == 0 || (b) == 0xFF)
 
 const Byte kMaskToAllowedStatus[8] = {1, 1, 1, 0, 1, 0, 0, 0};
 const Byte kMaskToBitNumber[8] = {0, 1, 2, 2, 3, 3, 3, 3};
 
 SizeT x86_Convert(Byte *data, SizeT size, UInt32 ip, UInt32 *state, int encoding)
 {
   SizeT bufferPos = 0, prevPosT;
   UInt32 prevMask = *state & 0x7;
   if (size < 5)
     return 0;
   ip += 5;
   prevPosT = (SizeT)0 - 1;
 
   for (;;)
   {
     Byte *p = data + bufferPos;
     Byte *limit = data + size - 4;
     for (; p < limit; p++)
       if ((*p & 0xFE) == 0xE8)
         break;
     bufferPos = (SizeT)(p - data);
     if (p >= limit)
       break;
     prevPosT = bufferPos - prevPosT;
     if (prevPosT > 3)
       prevMask = 0;
     else
     {
       prevMask = (prevMask << ((int)prevPosT - 1)) & 0x7;
       if (prevMask != 0)
       {
         Byte b = p[4 - kMaskToBitNumber[prevMask]];
         if (!kMaskToAllowedStatus[prevMask] || Test86MSByte(b))
         {
           prevPosT = bufferPos;
           prevMask = ((prevMask << 1) & 0x7) | 1;
           bufferPos++;
           continue;
         }
       }
     }
     prevPosT = bufferPos;
 
     if (Test86MSByte(p[4]))
     {
       UInt32 src = ((UInt32)p[4] << 24) | ((UInt32)p[3] << 16) | ((UInt32)p[2] << 8) | ((UInt32)p[1]);
       UInt32 dest;
       for (;;)
       {
         Byte b;
         int index;
         if (encoding)
           dest = (ip + (UInt32)bufferPos) + src;
         else
           dest = src - (ip + (UInt32)bufferPos);
         if (prevMask == 0)
           break;
         index = kMaskToBitNumber[prevMask] * 8;
         b = (Byte)(dest >> (24 - index));
         if (!Test86MSByte(b))
           break;
         src = dest ^ ((1 << (32 - index)) - 1);
       }
       p[4] = (Byte)(~(((dest >> 24) & 1) - 1));
       p[3] = (Byte)(dest >> 16);
       p[2] = (Byte)(dest >> 8);
       p[1] = (Byte)dest;
       bufferPos += 5;
     }
     else
     {
       prevMask = ((prevMask << 1) & 0x7) | 1;
       bufferPos++;
     }
   }
   prevPosT = bufferPos - prevPosT;
   *state = ((prevPosT > 3) ? 0 : ((prevMask << ((int)prevPosT - 1)) & 0x7));
   return bufferPos;
 }