1/// Given an array containing the number of codes of each code length,
2/// this function generates the huffman codes lengths and their respective
3/// code lengths as specified by the JPEG spec.
4const fn derive_codes_and_sizes(bits: &[u8; 16]) -> ([u8; 256], [u16; 256]) {
5 let mut huffsize = [0u8; 256];
6 let mut huffcode = [0u16; 256];
7
8 let mut k = 0;
9
10 // Annex C.2
11 // Figure C.1
12 // Generate table of individual code lengths
13 let mut i = 0;
14 while i < 16 {
15 let mut j = 0;
16 while j < bits[i as usize] {
17 huffsize[k] = i + 1;
18 k += 1;
19 j += 1;
20 }
21 i += 1;
22 }
23
24 huffsize[k] = 0;
25
26 // Annex C.2
27 // Figure C.2
28 // Generate table of huffman codes
29 k = 0;
30 let mut code = 0u16;
31 let mut size = huffsize[0];
32
33 while huffsize[k] != 0 {
34 huffcode[k] = code;
35 code += 1;
36 k += 1;
37
38 if huffsize[k] == size {
39 continue;
40 }
41
42 // FIXME there is something wrong with this code
43 let diff = huffsize[k].wrapping_sub(size);
44 code = if diff < 16 { code << diff as usize } else { 0 };
45
46 size = size.wrapping_add(diff);
47 }
48
49 (huffsize, huffcode)
50}
51
52pub(crate) const fn build_huff_lut_const(bits: &[u8; 16], huffval: &[u8]) -> [(u8, u16); 256] {
53 let mut lut: [(u8, u16); 256] = [(17u8, 0u16); 256];
54 let (huffsize: [u8; 256], huffcode: [u16; 256]) = derive_codes_and_sizes(bits);
55
56 let mut i: usize = 0;
57 while i < huffval.len() {
58 lut[huffval[i] as usize] = (huffsize[i], huffcode[i]);
59 i += 1;
60 }
61
62 lut
63}
64