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1 | #[derive(Clone,Copy,Default)] | |
2 | pub struct ProbCounter { | |
3 | zeroes: u32, | |
4 | total: u32, | |
5 | } | |
6 | ||
7 | // bits to code zero probability multiplied by eight | |
8 | pub const PROB_BITS: [u8; 256] = [ | |
9 | 0, 64, 56, 51, 48, 45, 43, 42, | |
10 | 40, 39, 37, 36, 35, 34, 34, 33, | |
11 | 32, 31, 31, 30, 29, 29, 28, 28, | |
12 | 27, 27, 26, 26, 26, 25, 25, 24, | |
13 | 24, 24, 23, 23, 23, 22, 22, 22, | |
14 | 21, 21, 21, 21, 20, 20, 20, 20, | |
15 | 19, 19, 19, 19, 18, 18, 18, 18, | |
16 | 18, 17, 17, 17, 17, 17, 16, 16, | |
17 | 16, 16, 16, 15, 15, 15, 15, 15, | |
18 | 15, 14, 14, 14, 14, 14, 14, 14, | |
19 | 13, 13, 13, 13, 13, 13, 13, 12, | |
20 | 12, 12, 12, 12, 12, 12, 12, 11, | |
21 | 11, 11, 11, 11, 11, 11, 11, 11, | |
22 | 10, 10, 10, 10, 10, 10, 10, 10, | |
23 | 10, 9, 9, 9, 9, 9, 9, 9, | |
24 | 9, 9, 9, 8, 8, 8, 8, 8, | |
25 | 8, 8, 8, 8, 8, 8, 7, 7, | |
26 | 7, 7, 7, 7, 7, 7, 7, 7, | |
27 | 7, 7, 6, 6, 6, 6, 6, 6, | |
28 | 6, 6, 6, 6, 6, 6, 6, 5, | |
29 | 5, 5, 5, 5, 5, 5, 5, 5, | |
30 | 5, 5, 5, 5, 5, 5, 4, 4, | |
31 | 4, 4, 4, 4, 4, 4, 4, 4, | |
32 | 4, 4, 4, 4, 4, 4, 3, 3, | |
33 | 3, 3, 3, 3, 3, 3, 3, 3, | |
34 | 3, 3, 3, 3, 3, 3, 3, 2, | |
35 | 2, 2, 2, 2, 2, 2, 2, 2, | |
36 | 2, 2, 2, 2, 2, 2, 2, 2, | |
37 | 2, 1, 1, 1, 1, 1, 1, 1, | |
38 | 1, 1, 1, 1, 1, 1, 1, 1, | |
39 | 1, 1, 1, 1, 1, 1, 0, 0, | |
40 | 0, 0, 0, 0, 0, 0, 0, 0 | |
41 | ]; | |
42 | ||
43 | impl ProbCounter { | |
44 | pub fn add(&mut self, b: bool) { | |
45 | if !b { | |
46 | self.zeroes += 1; | |
47 | } | |
48 | self.total += 1; | |
49 | } | |
50 | pub fn to_prob(self) -> u8 { | |
51 | if self.total > 0 { | |
52 | (((self.zeroes << 8) / self.total).min(254) & !1).max(1) as u8 | |
53 | } else { | |
54 | 128 | |
55 | } | |
56 | } | |
57 | pub fn to_prob_worthy(&self, old_prob: u8) -> u8 { | |
58 | if self.total > 0 { | |
59 | let new_prob = self.to_prob(); | |
60 | let new_bits = Self::est_bits(new_prob, self.zeroes, self.total); | |
61 | let old_bits = Self::est_bits(old_prob, self.zeroes, self.total); | |
62 | ||
63 | if new_bits + 7 < old_bits { | |
64 | new_prob | |
65 | } else { | |
66 | old_prob | |
67 | } | |
68 | } else { | |
69 | old_prob | |
70 | } | |
71 | } | |
72 | fn est_bits(prob: u8, zeroes: u32, total: u32) -> u32 { | |
73 | (u32::from(PROB_BITS[prob as usize]) * zeroes + u32::from(PROB_BITS[256 - (prob as usize)]) * (total - zeroes) + 7) >> 3 | |
74 | } | |
75 | } |