h264_decoder/
utils.rs

1use super::errors::H264Error;
2use bytesio::bits_reader::BitsReader;
3
4// ue(v) in 9.1 Parsing process for Exp-Golomb codes
5// ISO_IEC_14496-10-AVC-2012.pdf, page 227.
6// Syntax elements coded as ue(v), me(v), or se(v) are Exp-Golomb-coded.
7//      leadingZeroBits = -1;
8//      for( b = 0; !b; leadingZeroBits++ )
9//          b = read_bits( 1 )
10// The variable codeNum is then assigned as follows:
11//      codeNum = (2<<leadingZeroBits) - 1 + read_bits( leadingZeroBits )
12pub fn read_uev(bit_reader: &mut BitsReader) -> Result<u32, H264Error> {
13    let mut leading_zeros_bits: usize = 0;
14
15    loop {
16        if bit_reader.read_bit()? != 0 {
17            break;
18        }
19        leading_zeros_bits += 1;
20    }
21    let code_num = (1 << leading_zeros_bits) - 1 + bit_reader.read_n_bits(leading_zeros_bits)?;
22    Ok(code_num as u32)
23}
24
25// ISO_IEC_14496-10-AVC-2012.pdf, page 229.
26pub fn read_sev(bit_reader: &mut BitsReader) -> Result<i32, H264Error> {
27    let code_num = read_uev(bit_reader)?;
28
29    let negative: i64 = if code_num % 2 == 0 { -1 } else { 1 };
30    let se_value = (code_num as i64 + 1) / 2 * negative;
31    Ok(se_value as i32)
32}
33
34#[cfg(test)]
35mod tests {
36
37    use super::read_uev;
38    use bytes::BytesMut;
39    use bytesio::bits_reader::BitsReader;
40    use bytesio::bytes_reader::BytesReader;
41
42    #[test]
43    fn test_read_uev() {
44        // 0 => 1 => 1
45        // 1 => 10 => 010
46        // 2 => 11 => 011
47        // 3 => 100 => 00100
48        // 4 => 101 => 00101
49        // 5 => 110 => 00110
50        // 6 => 111 => 00111
51        // 7 => 1000 => 0001000
52        // 8 => 1001 => 0001001
53
54        let mut bytes_reader = BytesReader::new(BytesMut::new());
55        bytes_reader.extend_from_slice(&[0b00000001]);
56        bytes_reader.extend_from_slice(&[0b00000010]);
57        bytes_reader.extend_from_slice(&[0b00000011]);
58        bytes_reader.extend_from_slice(&[0b00000100]);
59        bytes_reader.extend_from_slice(&[0b00000101]);
60        bytes_reader.extend_from_slice(&[0b00000110]);
61        bytes_reader.extend_from_slice(&[0b00000111]);
62        bytes_reader.extend_from_slice(&[0b00001000]);
63        bytes_reader.extend_from_slice(&[0b00001001]);
64
65        let mut bits_reader = BitsReader::new(bytes_reader);
66
67        bits_reader.read_n_bits(7).unwrap();
68        let v1 = read_uev(&mut bits_reader).unwrap();
69        println!("=={v1}==");
70        assert!(v1 == 0);
71
72        bits_reader.read_n_bits(5).unwrap();
73        let v2 = read_uev(&mut bits_reader).unwrap();
74        println!("=={v2}==");
75        assert!(v2 == 1);
76
77        bits_reader.read_n_bits(5).unwrap();
78        let v3 = read_uev(&mut bits_reader).unwrap();
79        println!("=={v3}==");
80        assert!(v3 == 2);
81
82        bits_reader.read_n_bits(3).unwrap();
83        let v4 = read_uev(&mut bits_reader).unwrap();
84        println!("=={v4}==");
85        assert!(v4 == 3);
86
87        bits_reader.read_n_bits(3).unwrap();
88        let v5 = read_uev(&mut bits_reader).unwrap();
89        println!("=={v5}==");
90        assert!(v5 == 4);
91
92        bits_reader.read_n_bits(3).unwrap();
93        let v6 = read_uev(&mut bits_reader).unwrap();
94        println!("=={v6}==");
95        assert!(v6 == 5);
96
97        bits_reader.read_n_bits(3).unwrap();
98        let v7 = read_uev(&mut bits_reader).unwrap();
99        println!("=={v7}==");
100        assert!(v7 == 6);
101
102        bits_reader.read_n_bits(1).unwrap();
103        let v8 = read_uev(&mut bits_reader).unwrap();
104        println!("=={v8}==");
105        assert!(v8 == 7);
106
107        bits_reader.read_n_bits(1).unwrap();
108        let v9 = read_uev(&mut bits_reader).unwrap();
109        println!("=={v9}==");
110        assert!(v9 == 8);
111    }
112}
h264_decoder/utils.rs

h264_decoder/
utils.rs
