b24e7fce |
1 | /* Delta.c -- Delta converter |
2 | 2009-05-26 : Igor Pavlov : Public domain */ |
3 | |
4 | #include "Precomp.h" |
5 | |
6 | #include "Delta.h" |
7 | |
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 | |
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 | |
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 | |
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 | } |