nihav-duck/src/codecs/vpenc/models.rs

   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 }