`nx_jpeg_sym.nx` source

1// nx_jpeg_sym.nx -- SOVEREIGN JPEG "modeling" layer: separates a block's entropy into (a) a SYMBOL stream
2// (DC categories + AC (run<<4|size) bytes + EOB/ZRL) and (b) the raw sign-magnitude additional bits. This
3// is exactly the modeling JPEG does before Huffman -- but here the symbols are emitted as plain bytes so a
4// DIFFERENT final coder (our rANS) can entropy-code them. Comparing rANS(symbols) vs Huffman(symbols) with
5// identical magnitude bits isolates the pure entropy-coder question at identical quality. Reuses the J1
6// substrate (jhe_mag_cat / jhe_mag_bits / jhe_decode_mag) over nx_h264_bitwriter. license_tier: ORIGINAL
7import "nx_syscalls.nx"
8import "nx_h264_bitwriter.nx"
9import "nx_jpeg_huff_enc.nx"
10
11// Encode zz[64] (zigzag, zz[0]=DC) -> append symbol bytes to sym[] (sp[0] = running count), and the
12// sign-magnitude additional bits to bwmag. prevdc = previous block's DC. Returns this block's DC.
13func jsym_encode_block(sym: *u8, sp: *i64, bwmag: *BitWriter, zz: *i64, prevdc: i64) -> i64 {
14    var p: i64 = sp[0]
15    let diff: i64 = zz[0] - prevdc
16    let dccat: i64 = jhe_mag_cat(diff)
17    sym[p] = dccat as u8; p = p + 1
18    if dccat > 0 { bw_write_bits(bwmag, jhe_mag_bits(diff, dccat), dccat) }
19    var run: i64 = 0
20    var k: i64 = 1
21    while k < 64 {
22        let v: i64 = zz[k]
23        if v == 0 { run = run + 1 } else {
24            while run >= 16 { sym[p] = 0xF0 as u8; p = p + 1; run = run - 16 }
25            let cat: i64 = jhe_mag_cat(v)
26            let s: i64 = (run << 4) | cat
27            sym[p] = s as u8; p = p + 1
28            if cat > 0 { bw_write_bits(bwmag, jhe_mag_bits(v, cat), cat) }
29            run = 0
30        }
31        k = k + 1
32    }
33    if run > 0 { sym[p] = 0x00 as u8; p = p + 1 }
34    sp[0] = p
35    return zz[0]
36}
37
38// Decode one block: read symbol bytes from sym[] (sp[0] running index) + magnitude bits from magbuf at
39// magpos -> zz[64]. prevdc = previous DC. Returns this block's DC.
40func jsym_decode_block(sym: *u8, sp: *i64, magbuf: *u8, magpos: *i64, prevdc: i64, zz: *i64) -> i64 {
41    var i: i64 = 0
42    while i < 64 { zz[i] = 0; i = i + 1 }
43    var p: i64 = sp[0]
44    let dccat: i64 = sym[p] as i64; p = p + 1
45    let dc: i64 = prevdc + jhe_decode_mag(magbuf, magpos, dccat)
46    zz[0] = dc
47    var k: i64 = 1
48    while k < 64 {
49        let s: i64 = sym[p] as i64; p = p + 1
50        if s == 0 { k = 64 } else {
51            let run: i64 = s >> 4
52            let size: i64 = s & 0xf
53            if size == 0 { k = k + 16 } else {
54                k = k + run
55                if k < 64 { zz[k] = jhe_decode_mag(magbuf, magpos, size); k = k + 1 }
56            }
57        }
58    }
59    sp[0] = p
60    return dc
61}
nx_jpeg_sym.nx source

`nx_jpeg_sym.nx` source
