1 /* Delta.c -- Delta converter
2 2009-05-26 : Igor Pavlov : Public domain */
3 
4 #include "Precomp.h"
5 
6 #include "Delta.h"
7 
Delta_Init(Byte * state)8 void Delta_Init(Byte *state)
9 {
10   unsigned i;
11   for (i = 0; i < DELTA_STATE_SIZE; i++)
12     state[i] = 0;
13 }
14 
MyMemCpy(Byte * dest,const Byte * src,unsigned size)15 static void MyMemCpy(Byte *dest, const Byte *src, unsigned size)
16 {
17   unsigned i;
18   for (i = 0; i < size; i++)
19     dest[i] = src[i];
20 }
21 
Delta_Encode(Byte * state,unsigned delta,Byte * data,SizeT size)22 void Delta_Encode(Byte *state, unsigned delta, Byte *data, SizeT size)
23 {
24   Byte buf[DELTA_STATE_SIZE];
25   unsigned j = 0;
26   MyMemCpy(buf, state, delta);
27   {
28     SizeT i;
29     for (i = 0; i < size;)
30     {
31       for (j = 0; j < delta && i < size; i++, j++)
32       {
33         Byte b = data[i];
34         data[i] = (Byte)(b - buf[j]);
35         buf[j] = b;
36       }
37     }
38   }
39   if (j == delta)
40     j = 0;
41   MyMemCpy(state, buf + j, delta - j);
42   MyMemCpy(state + delta - j, buf, j);
43 }
44 
Delta_Decode(Byte * state,unsigned delta,Byte * data,SizeT size)45 void Delta_Decode(Byte *state, unsigned delta, Byte *data, SizeT size)
46 {
47   Byte buf[DELTA_STATE_SIZE];
48   unsigned j = 0;
49   MyMemCpy(buf, state, delta);
50   {
51     SizeT i;
52     for (i = 0; i < size;)
53     {
54       for (j = 0; j < delta && i < size; i++, j++)
55       {
56         buf[j] = data[i] = (Byte)(buf[j] + data[i]);
57       }
58     }
59   }
60   if (j == delta)
61     j = 0;
62   MyMemCpy(state, buf + j, delta - j);
63   MyMemCpy(state + delta - j, buf, j);
64 }
65