tor-browser

Bcj2.c (6351B)

---

/* Bcj2.c -- BCJ2 Decoder (Converter for x86 code)
2018-04-28 : Igor Pavlov : Public domain */

#include "Precomp.h"

#include "Bcj2.h"
#include "CpuArch.h"

#define CProb UInt16

#define kTopValue ((UInt32)1 << 24)
#define kNumModelBits 11
#define kBitModelTotal (1 << kNumModelBits)
#define kNumMoveBits 5

#define _IF_BIT_0 ttt = *prob; bound = (p->range >> kNumModelBits) * ttt; if (p->code < bound)
#define _UPDATE_0 p->range = bound; *prob = (CProb)(ttt + ((kBitModelTotal - ttt) >> kNumMoveBits));
#define _UPDATE_1 p->range -= bound; p->code -= bound; *prob = (CProb)(ttt - (ttt >> kNumMoveBits));

void Bcj2Dec_Init(CBcj2Dec *p)
{
 unsigned i;

 p->state = BCJ2_DEC_STATE_OK;
 p->ip = 0;
 p->temp[3] = 0;
 p->range = 0;
 p->code = 0;
 for (i = 0; i < sizeof(p->probs) / sizeof(p->probs[0]); i++)
   p->probs[i] = kBitModelTotal >> 1;
}

SRes Bcj2Dec_Decode(CBcj2Dec *p)
{
 if (p->range <= 5)
 {
   p->state = BCJ2_DEC_STATE_OK;
   for (; p->range != 5; p->range++)
   {
     if (p->range == 1 && p->code != 0)
       return SZ_ERROR_DATA;
     
     if (p->bufs[BCJ2_STREAM_RC] == p->lims[BCJ2_STREAM_RC])
     {
       p->state = BCJ2_STREAM_RC;
       return SZ_OK;
     }

     p->code = (p->code << 8) | *(p->bufs[BCJ2_STREAM_RC])++;
   }
   
   if (p->code == 0xFFFFFFFF)
     return SZ_ERROR_DATA;
   
   p->range = 0xFFFFFFFF;
 }
 else if (p->state >= BCJ2_DEC_STATE_ORIG_0)
 {
   while (p->state <= BCJ2_DEC_STATE_ORIG_3)
   {
     Byte *dest = p->dest;
     if (dest == p->destLim)
       return SZ_OK;
     *dest = p->temp[(size_t)p->state - BCJ2_DEC_STATE_ORIG_0];
     p->state++;
     p->dest = dest + 1;
   }
 }

 /*
 if (BCJ2_IS_32BIT_STREAM(p->state))
 {
   const Byte *cur = p->bufs[p->state];
   if (cur == p->lims[p->state])
     return SZ_OK;
   p->bufs[p->state] = cur + 4;
   
   {
     UInt32 val;
     Byte *dest;
     SizeT rem;
     
     p->ip += 4;
     val = GetBe32(cur) - p->ip;
     dest = p->dest;
     rem = p->destLim - dest;
     if (rem < 4)
     {
       SizeT i;
       SetUi32(p->temp, val);
       for (i = 0; i < rem; i++)
         dest[i] = p->temp[i];
       p->dest = dest + rem;
       p->state = BCJ2_DEC_STATE_ORIG_0 + (unsigned)rem;
       return SZ_OK;
     }
     SetUi32(dest, val);
     p->temp[3] = (Byte)(val >> 24);
     p->dest = dest + 4;
     p->state = BCJ2_DEC_STATE_OK;
   }
 }
 */

 for (;;)
 {
   if (BCJ2_IS_32BIT_STREAM(p->state))
     p->state = BCJ2_DEC_STATE_OK;
   else
   {
     if (p->range < kTopValue)
     {
       if (p->bufs[BCJ2_STREAM_RC] == p->lims[BCJ2_STREAM_RC])
       {
         p->state = BCJ2_STREAM_RC;
         return SZ_OK;
       }
       p->range <<= 8;
       p->code = (p->code << 8) | *(p->bufs[BCJ2_STREAM_RC])++;
     }

     {
       const Byte *src = p->bufs[BCJ2_STREAM_MAIN];
       const Byte *srcLim;
       Byte *dest;
       SizeT num = p->lims[BCJ2_STREAM_MAIN] - src;
       
       if (num == 0)
       {
         p->state = BCJ2_STREAM_MAIN;
         return SZ_OK;
       }
       
       dest = p->dest;
       if (num > (SizeT)(p->destLim - dest))
       {
         num = p->destLim - dest;
         if (num == 0)
         {
           p->state = BCJ2_DEC_STATE_ORIG;
           return SZ_OK;
         }
       }
      
       srcLim = src + num;

       if (p->temp[3] == 0x0F && (src[0] & 0xF0) == 0x80)
         *dest = src[0];
       else for (;;)
       {
         Byte b = *src;
         *dest = b;
         if (b != 0x0F)
         {
           if ((b & 0xFE) == 0xE8)
             break;
           dest++;
           if (++src != srcLim)
             continue;
           break;
         }
         dest++;
         if (++src == srcLim)
           break;
         if ((*src & 0xF0) != 0x80)
           continue;
         *dest = *src;
         break;
       }
       
       num = src - p->bufs[BCJ2_STREAM_MAIN];
       
       if (src == srcLim)
       {
         p->temp[3] = src[-1];
         p->bufs[BCJ2_STREAM_MAIN] = src;
         p->ip += (UInt32)num;
         p->dest += num;
         p->state =
           p->bufs[BCJ2_STREAM_MAIN] ==
           p->lims[BCJ2_STREAM_MAIN] ?
             (unsigned)BCJ2_STREAM_MAIN :
             (unsigned)BCJ2_DEC_STATE_ORIG;
         return SZ_OK;
       }
       
       {
         UInt32 bound, ttt;
         CProb *prob;
         Byte b = src[0];
         Byte prev = (Byte)(num == 0 ? p->temp[3] : src[-1]);
         
         p->temp[3] = b;
         p->bufs[BCJ2_STREAM_MAIN] = src + 1;
         num++;
         p->ip += (UInt32)num;
         p->dest += num;
         
         prob = p->probs + (unsigned)(b == 0xE8 ? 2 + (unsigned)prev : (b == 0xE9 ? 1 : 0));
         
         _IF_BIT_0
         {
           _UPDATE_0
           continue;
         }
         _UPDATE_1
           
       }
     }
   }

   {
     UInt32 val;
     unsigned cj = (p->temp[3] == 0xE8) ? BCJ2_STREAM_CALL : BCJ2_STREAM_JUMP;
     const Byte *cur = p->bufs[cj];
     Byte *dest;
     SizeT rem;
     
     if (cur == p->lims[cj])
     {
       p->state = cj;
       break;
     }
     
     val = GetBe32(cur);
     p->bufs[cj] = cur + 4;

     p->ip += 4;
     val -= p->ip;
     dest = p->dest;
     rem = p->destLim - dest;
     
     if (rem < 4)
     {
       p->temp[0] = (Byte)val; if (rem > 0) dest[0] = (Byte)val; val >>= 8;
       p->temp[1] = (Byte)val; if (rem > 1) dest[1] = (Byte)val; val >>= 8;
       p->temp[2] = (Byte)val; if (rem > 2) dest[2] = (Byte)val; val >>= 8;
       p->temp[3] = (Byte)val;
       p->dest = dest + rem;
       p->state = BCJ2_DEC_STATE_ORIG_0 + (unsigned)rem;
       break;
     }
     
     SetUi32(dest, val);
     p->temp[3] = (Byte)(val >> 24);
     p->dest = dest + 4;
   }
 }

 if (p->range < kTopValue && p->bufs[BCJ2_STREAM_RC] != p->lims[BCJ2_STREAM_RC])
 {
   p->range <<= 8;
   p->code = (p->code << 8) | *(p->bufs[BCJ2_STREAM_RC])++;
 }

 return SZ_OK;
}