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implement simplified prob update, update unpack.c

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This commit is contained in:
Dennis Ranke
2022-09-10 12:01:42 +02:00
parent 36cb6d77b5
commit f1f1c64a76
2 changed files with 20 additions and 18 deletions
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13
src/context_state.rs
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@@ -1,8 +1,8 @@
use crate::rans::{ONE_PROB, PROB_BITS};
const INIT_PROB: u16 = 1 << (PROB_BITS - 1);
const UPDATE_RATE: u32 = 4;
const UPDATE_ADD: u32 = 8;
const UPDATE_RATE: i32 = 4;
const UPDATE_ADD: i32 = 8;
#[derive(Clone)]
pub struct ContextState {
@@ -33,10 +33,13 @@ impl<'a> Context<'a> {
pub fn update(&mut self, bit: bool) {
let old = self.state.contexts[self.index];
self.state.contexts[self.index] = if !bit {
old + ((ONE_PROB - old as u32 + UPDATE_ADD) >> UPDATE_RATE) as u8
let offset = if !bit {
ONE_PROB as i32 >> UPDATE_RATE
} else {
old - ((old as u32 + UPDATE_ADD) >> UPDATE_RATE) as u8
0
};
self.state.contexts[self.index] =
(offset + old as i32 - ((old as i32 + UPDATE_ADD) >> UPDATE_RATE)) as u8;
}
}