9e052883 |
1 | /* Delta.c -- Delta converter\r |
2 | 2021-02-09 : Igor Pavlov : Public domain */\r |
3 | \r |
4 | #include "Precomp.h"\r |
5 | \r |
6 | #include "Delta.h"\r |
7 | \r |
8 | void Delta_Init(Byte *state)\r |
9 | {\r |
10 | unsigned i;\r |
11 | for (i = 0; i < DELTA_STATE_SIZE; i++)\r |
12 | state[i] = 0;\r |
13 | }\r |
14 | \r |
15 | \r |
16 | void Delta_Encode(Byte *state, unsigned delta, Byte *data, SizeT size)\r |
17 | {\r |
18 | Byte temp[DELTA_STATE_SIZE];\r |
19 | \r |
20 | if (size == 0)\r |
21 | return;\r |
22 | \r |
23 | {\r |
24 | unsigned i = 0;\r |
25 | do\r |
26 | temp[i] = state[i];\r |
27 | while (++i != delta);\r |
28 | }\r |
29 | \r |
30 | if (size <= delta)\r |
31 | {\r |
32 | unsigned i = 0, k;\r |
33 | do\r |
34 | {\r |
35 | Byte b = *data;\r |
36 | *data++ = (Byte)(b - temp[i]);\r |
37 | temp[i] = b;\r |
38 | }\r |
39 | while (++i != size);\r |
40 | \r |
41 | k = 0;\r |
42 | \r |
43 | do\r |
44 | {\r |
45 | if (i == delta)\r |
46 | i = 0;\r |
47 | state[k] = temp[i++];\r |
48 | }\r |
49 | while (++k != delta);\r |
50 | \r |
51 | return;\r |
52 | }\r |
53 | \r |
54 | {\r |
55 | Byte *p = data + size - delta;\r |
56 | {\r |
57 | unsigned i = 0;\r |
58 | do\r |
59 | state[i] = *p++;\r |
60 | while (++i != delta);\r |
61 | }\r |
62 | {\r |
63 | const Byte *lim = data + delta;\r |
64 | ptrdiff_t dif = -(ptrdiff_t)delta;\r |
65 | \r |
66 | if (((ptrdiff_t)size + dif) & 1)\r |
67 | {\r |
68 | --p; *p = (Byte)(*p - p[dif]);\r |
69 | }\r |
70 | \r |
71 | while (p != lim)\r |
72 | {\r |
73 | --p; *p = (Byte)(*p - p[dif]);\r |
74 | --p; *p = (Byte)(*p - p[dif]);\r |
75 | }\r |
76 | \r |
77 | dif = -dif;\r |
78 | \r |
79 | do\r |
80 | {\r |
81 | --p; *p = (Byte)(*p - temp[--dif]);\r |
82 | }\r |
83 | while (dif != 0);\r |
84 | }\r |
85 | }\r |
86 | }\r |
87 | \r |
88 | \r |
89 | void Delta_Decode(Byte *state, unsigned delta, Byte *data, SizeT size)\r |
90 | {\r |
91 | unsigned i;\r |
92 | const Byte *lim;\r |
93 | \r |
94 | if (size == 0)\r |
95 | return;\r |
96 | \r |
97 | i = 0;\r |
98 | lim = data + size;\r |
99 | \r |
100 | if (size <= delta)\r |
101 | {\r |
102 | do\r |
103 | *data = (Byte)(*data + state[i++]);\r |
104 | while (++data != lim);\r |
105 | \r |
106 | for (; delta != i; state++, delta--)\r |
107 | *state = state[i];\r |
108 | data -= i;\r |
109 | }\r |
110 | else\r |
111 | {\r |
112 | /*\r |
113 | #define B(n) b ## n\r |
114 | #define I(n) Byte B(n) = state[n];\r |
115 | #define U(n) { B(n) = (Byte)((B(n)) + *data++); data[-1] = (B(n)); }\r |
116 | #define F(n) if (data != lim) { U(n) }\r |
117 | \r |
118 | if (delta == 1)\r |
119 | {\r |
120 | I(0)\r |
121 | if ((lim - data) & 1) { U(0) }\r |
122 | while (data != lim) { U(0) U(0) }\r |
123 | data -= 1;\r |
124 | }\r |
125 | else if (delta == 2)\r |
126 | {\r |
127 | I(0) I(1)\r |
128 | lim -= 1; while (data < lim) { U(0) U(1) }\r |
129 | lim += 1; F(0)\r |
130 | data -= 2;\r |
131 | }\r |
132 | else if (delta == 3)\r |
133 | {\r |
134 | I(0) I(1) I(2)\r |
135 | lim -= 2; while (data < lim) { U(0) U(1) U(2) }\r |
136 | lim += 2; F(0) F(1)\r |
137 | data -= 3;\r |
138 | }\r |
139 | else if (delta == 4)\r |
140 | {\r |
141 | I(0) I(1) I(2) I(3)\r |
142 | lim -= 3; while (data < lim) { U(0) U(1) U(2) U(3) }\r |
143 | lim += 3; F(0) F(1) F(2)\r |
144 | data -= 4;\r |
145 | }\r |
146 | else\r |
147 | */\r |
148 | {\r |
149 | do\r |
150 | {\r |
151 | *data = (Byte)(*data + state[i++]);\r |
152 | data++;\r |
153 | }\r |
154 | while (i != delta);\r |
155 | \r |
156 | {\r |
157 | ptrdiff_t dif = -(ptrdiff_t)delta;\r |
158 | do\r |
159 | *data = (Byte)(*data + data[dif]);\r |
160 | while (++data != lim);\r |
161 | data += dif;\r |
162 | }\r |
163 | }\r |
164 | }\r |
165 | \r |
166 | do\r |
167 | *state++ = *data;\r |
168 | while (++data != lim);\r |
169 | }\r |