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