1 #include	<u.h>
2 #include	<libc.h>
3 #include	<bio.h>
4 #include	"sky.h"
5 
6 static int hufvals[] = {
7 	 1,  1,  1,  1,  1,  1,  1,  1,
8 	 2,  2,  2,  2,  2,  2,  2,  2,
9 	 4,  4,  4,  4,  4,  4,  4,  4,
10 	 8,  8,  8,  8,  8,  8,  8,  8,
11 	 3,  3,  3,  3,  5,  5,  5,  5,
12 	10, 10, 10, 10, 12, 12, 12, 12,
13 	15, 15, 15, 15,  6,  6,  7,  7,
14 	 9,  9, 11, 11, 13, 13,  0, 14
15 };
16 
17 static int huflens[] = {
18 	3, 3, 3, 3, 3, 3, 3, 3,
19 	3, 3, 3, 3, 3, 3, 3, 3,
20 	3, 3, 3, 3, 3, 3, 3, 3,
21 	3, 3, 3, 3, 3, 3, 3, 3,
22 	4, 4, 4, 4, 4, 4, 4, 4,
23 	4, 4, 4, 4, 4, 4, 4, 4,
24 	4, 4, 4, 4, 5, 5, 5, 5,
25 	5, 5, 5, 5, 5, 5, 6, 6
26 };
27 
28 static	int	buffer;
29 static	int	bits_to_go;		/* Number of bits still in buffer */
30 
31 void
32 start_inputing_bits(void)
33 {
34 	bits_to_go = 0;
35 }
36 
37 int
38 input_huffman(Biobuf *infile)
39 {
40 	int c;
41 
42 	if(bits_to_go < 6) {
43 		c = Bgetc(infile);
44 		if(c < 0) {
45 			fprint(2, "input_huffman: unexpected EOF\n");
46 			exits("format");
47 		}
48 		buffer = (buffer<<8) | c;
49 		bits_to_go += 8;
50 	}
51 	c = (buffer >> (bits_to_go-6)) & 0x3f;
52 	bits_to_go -= huflens[c];
53 	return hufvals[c];
54 }
55 
56 int
57 input_nybble(Biobuf *infile)
58 {
59 	int c;
60 
61 	if(bits_to_go < 4) {
62 		c = Bgetc(infile);
63 		if(c < 0){
64 			fprint(2, "input_nybble: unexpected EOF\n");
65 			exits("format");
66 		}
67 		buffer = (buffer<<8) | c;
68 		bits_to_go += 8;
69 	}
70 
71 	/*
72 	 * pick off the first 4 bits
73 	 */
74 	bits_to_go -= 4;
75 	return (buffer>>bits_to_go) & 0x0f;
76 }