1 /* Bcj2.c -- BCJ2 Decoder (Converter for x86 code)
2 2018-04-28 : Igor Pavlov : Public domain */
3 
4 #include "Precomp.h"
5 
6 #include "Bcj2.h"
7 #include "CpuArch.h"
8 
9 #define CProb UInt16
10 
11 #define kTopValue ((UInt32)1 << 24)
12 #define kNumModelBits 11
13 #define kBitModelTotal (1 << kNumModelBits)
14 #define kNumMoveBits 5
15 
16 #define _IF_BIT_0 ttt = *prob; bound = (p->range >> kNumModelBits) * ttt; if (p->code < bound)
17 #define _UPDATE_0 p->range = bound; *prob = (CProb)(ttt + ((kBitModelTotal - ttt) >> kNumMoveBits));
18 #define _UPDATE_1 p->range -= bound; p->code -= bound; *prob = (CProb)(ttt - (ttt >> kNumMoveBits));
19 
Bcj2Dec_Init(CBcj2Dec * p)20 void Bcj2Dec_Init(CBcj2Dec *p)
21 {
22   unsigned i;
23 
24   p->state = BCJ2_DEC_STATE_OK;
25   p->ip = 0;
26   p->temp[3] = 0;
27   p->range = 0;
28   p->code = 0;
29   for (i = 0; i < sizeof(p->probs) / sizeof(p->probs[0]); i++)
30     p->probs[i] = kBitModelTotal >> 1;
31 }
32 
Bcj2Dec_Decode(CBcj2Dec * p)33 SRes Bcj2Dec_Decode(CBcj2Dec *p)
34 {
35   if (p->range <= 5)
36   {
37     p->state = BCJ2_DEC_STATE_OK;
38     for (; p->range != 5; p->range++)
39     {
40       if (p->range == 1 && p->code != 0)
41         return SZ_ERROR_DATA;
42 
43       if (p->bufs[BCJ2_STREAM_RC] == p->lims[BCJ2_STREAM_RC])
44       {
45         p->state = BCJ2_STREAM_RC;
46         return SZ_OK;
47       }
48 
49       p->code = (p->code << 8) | *(p->bufs[BCJ2_STREAM_RC])++;
50     }
51 
52     if (p->code == 0xFFFFFFFF)
53       return SZ_ERROR_DATA;
54 
55     p->range = 0xFFFFFFFF;
56   }
57   else if (p->state >= BCJ2_DEC_STATE_ORIG_0)
58   {
59     while (p->state <= BCJ2_DEC_STATE_ORIG_3)
60     {
61       Byte *dest = p->dest;
62       if (dest == p->destLim)
63         return SZ_OK;
64       *dest = p->temp[(size_t)p->state - BCJ2_DEC_STATE_ORIG_0];
65       p->state++;
66       p->dest = dest + 1;
67     }
68   }
69 
70   /*
71   if (BCJ2_IS_32BIT_STREAM(p->state))
72   {
73     const Byte *cur = p->bufs[p->state];
74     if (cur == p->lims[p->state])
75       return SZ_OK;
76     p->bufs[p->state] = cur + 4;
77 
78     {
79       UInt32 val;
80       Byte *dest;
81       SizeT rem;
82 
83       p->ip += 4;
84       val = GetBe32(cur) - p->ip;
85       dest = p->dest;
86       rem = p->destLim - dest;
87       if (rem < 4)
88       {
89         SizeT i;
90         SetUi32(p->temp, val);
91         for (i = 0; i < rem; i++)
92           dest[i] = p->temp[i];
93         p->dest = dest + rem;
94         p->state = BCJ2_DEC_STATE_ORIG_0 + (unsigned)rem;
95         return SZ_OK;
96       }
97       SetUi32(dest, val);
98       p->temp[3] = (Byte)(val >> 24);
99       p->dest = dest + 4;
100       p->state = BCJ2_DEC_STATE_OK;
101     }
102   }
103   */
104 
105   for (;;)
106   {
107     if (BCJ2_IS_32BIT_STREAM(p->state))
108       p->state = BCJ2_DEC_STATE_OK;
109     else
110     {
111       if (p->range < kTopValue)
112       {
113         if (p->bufs[BCJ2_STREAM_RC] == p->lims[BCJ2_STREAM_RC])
114         {
115           p->state = BCJ2_STREAM_RC;
116           return SZ_OK;
117         }
118         p->range <<= 8;
119         p->code = (p->code << 8) | *(p->bufs[BCJ2_STREAM_RC])++;
120       }
121 
122       {
123         const Byte *src = p->bufs[BCJ2_STREAM_MAIN];
124         const Byte *srcLim;
125         Byte *dest;
126         SizeT num = p->lims[BCJ2_STREAM_MAIN] - src;
127 
128         if (num == 0)
129         {
130           p->state = BCJ2_STREAM_MAIN;
131           return SZ_OK;
132         }
133 
134         dest = p->dest;
135         if (num > (SizeT)(p->destLim - dest))
136         {
137           num = p->destLim - dest;
138           if (num == 0)
139           {
140             p->state = BCJ2_DEC_STATE_ORIG;
141             return SZ_OK;
142           }
143         }
144 
145         srcLim = src + num;
146 
147         if (p->temp[3] == 0x0F && (src[0] & 0xF0) == 0x80)
148           *dest = src[0];
149         else for (;;)
150         {
151           Byte b = *src;
152           *dest = b;
153           if (b != 0x0F)
154           {
155             if ((b & 0xFE) == 0xE8)
156               break;
157             dest++;
158             if (++src != srcLim)
159               continue;
160             break;
161           }
162           dest++;
163           if (++src == srcLim)
164             break;
165           if ((*src & 0xF0) != 0x80)
166             continue;
167           *dest = *src;
168           break;
169         }
170 
171         num = src - p->bufs[BCJ2_STREAM_MAIN];
172 
173         if (src == srcLim)
174         {
175           p->temp[3] = src[-1];
176           p->bufs[BCJ2_STREAM_MAIN] = src;
177           p->ip += (UInt32)num;
178           p->dest += num;
179           p->state =
180             p->bufs[BCJ2_STREAM_MAIN] ==
181             p->lims[BCJ2_STREAM_MAIN] ?
182               (unsigned)BCJ2_STREAM_MAIN :
183               (unsigned)BCJ2_DEC_STATE_ORIG;
184           return SZ_OK;
185         }
186 
187         {
188           UInt32 bound, ttt;
189           CProb *prob;
190           Byte b = src[0];
191           Byte prev = (Byte)(num == 0 ? p->temp[3] : src[-1]);
192 
193           p->temp[3] = b;
194           p->bufs[BCJ2_STREAM_MAIN] = src + 1;
195           num++;
196           p->ip += (UInt32)num;
197           p->dest += num;
198 
199           prob = p->probs + (unsigned)(b == 0xE8 ? 2 + (unsigned)prev : (b == 0xE9 ? 1 : 0));
200 
201           _IF_BIT_0
202           {
203             _UPDATE_0
204             continue;
205           }
206           _UPDATE_1
207 
208         }
209       }
210     }
211 
212     {
213       UInt32 val;
214       unsigned cj = (p->temp[3] == 0xE8) ? BCJ2_STREAM_CALL : BCJ2_STREAM_JUMP;
215       const Byte *cur = p->bufs[cj];
216       Byte *dest;
217       SizeT rem;
218 
219       if (cur == p->lims[cj])
220       {
221         p->state = cj;
222         break;
223       }
224 
225       val = GetBe32(cur);
226       p->bufs[cj] = cur + 4;
227 
228       p->ip += 4;
229       val -= p->ip;
230       dest = p->dest;
231       rem = p->destLim - dest;
232 
233       if (rem < 4)
234       {
235         p->temp[0] = (Byte)val; if (rem > 0) dest[0] = (Byte)val; val >>= 8;
236         p->temp[1] = (Byte)val; if (rem > 1) dest[1] = (Byte)val; val >>= 8;
237         p->temp[2] = (Byte)val; if (rem > 2) dest[2] = (Byte)val; val >>= 8;
238         p->temp[3] = (Byte)val;
239         p->dest = dest + rem;
240         p->state = BCJ2_DEC_STATE_ORIG_0 + (unsigned)rem;
241         break;
242       }
243 
244       SetUi32(dest, val);
245       p->temp[3] = (Byte)(val >> 24);
246       p->dest = dest + 4;
247     }
248   }
249 
250   if (p->range < kTopValue && p->bufs[BCJ2_STREAM_RC] != p->lims[BCJ2_STREAM_RC])
251   {
252     p->range <<= 8;
253     p->code = (p->code << 8) | *(p->bufs[BCJ2_STREAM_RC])++;
254   }
255 
256   return SZ_OK;
257 }
258