[WIP] experiment - compile-time precision

arithmetic-coding-core/src/model.rs

@@ -67,6 +67,14 @@ pub trait Model {
     /// The internal representation to use for storing integers
     type B: BitStore = u32;
 
+    /// The maximum denominator used for probability ranges. See
+    /// [`Model::probability`].
+    ///
+    /// This value is used to calculate an appropriate precision for the
+    /// encoding, therefore this value must not change, and
+    /// [`Model::denominator`] must never exceed it.
+    const MAX_DENOMINATOR: Self::B;
+
     /// Given a symbol, return an interval representing the probability of that
     /// symbol occurring.
     ///
@@ -98,17 +106,9 @@ pub trait Model {
     /// [`Encoder`](crate::Encoder) and [`Decoder`](crate::Decoder) to panic due
     /// to overflow or underflow.
     fn denominator(&self) -> Self::B {
-        self.max_denominator()
+        Self::MAX_DENOMINATOR
     }
 
-    /// The maximum denominator used for probability ranges. See
-    /// [`Model::probability`].
-    ///
-    /// This value is used to calculate an appropriate precision for the
-    /// encoding, therefore this value must not change, and
-    /// [`Model::denominator`] must never exceed it.
-    fn max_denominator(&self) -> Self::B;
-
     /// Given a value, return the symbol whose probability range it falls in.
     ///
     /// `None` indicates `EOF`

arithmetic-coding-core/src/model/fixed_length.rs

@@ -72,6 +72,14 @@ pub trait Model {
     /// The internal representation to use for storing integers
     type B: BitStore = u32;
 
+    /// The maximum denominator used for probability ranges. See
+    /// [`Model::probability`].
+    ///
+    /// This value is used to calculate an appropriate precision for the
+    /// encoding, therefore this value must not change, and
+    /// [`Model::denominator`] must never exceed it.
+    const MAX_DENOMINATOR: Self::B;
+
     /// Given a symbol, return an interval representing the probability of that
     /// symbol occurring.
     ///
@@ -100,17 +108,9 @@ pub trait Model {
     /// [`Encoder`](crate::Encoder) and [`Decoder`](crate::Decoder) to panic due
     /// to overflow or underflow.
     fn denominator(&self) -> Self::B {
-        self.max_denominator()
+        Self::MAX_DENOMINATOR
     }
 
-    /// The maximum denominator used for probability ranges. See
-    /// [`Model::probability`].
-    ///
-    /// This value is used to calculate an appropriate precision for the
-    /// encoding, therefore this value must not change, and
-    /// [`Model::denominator`] must never exceed it.
-    fn max_denominator(&self) -> Self::B;
-
     /// Given a value, return the symbol whose probability range it falls in.
     ///
     /// `None` indicates `EOF`
@@ -154,9 +154,11 @@ impl<M> crate::Model for Wrapper<M>
 where
     M: Model,
 {
-    type B = M::B;
     type Symbol = M::Symbol;
     type ValueError = Error<M::ValueError>;
+    type B = M::B;
+
+    const MAX_DENOMINATOR: Self::B = M::MAX_DENOMINATOR;
 
     fn probability(
         &self,
@@ -179,8 +181,8 @@ where
         }
     }
 
-    fn max_denominator(&self) -> Self::B {
-        self.model.max_denominator()
+    fn denominator(&self) -> Self::B {
+        self.model.denominator()
     }
 
     fn symbol(&self, value: Self::B) -> Option<Self::Symbol> {
@@ -191,10 +193,6 @@ where
         }
     }
 
-    fn denominator(&self) -> Self::B {
-        self.model.denominator()
-    }
-
     fn update(&mut self, symbol: Option<&Self::Symbol>) {
         if let Some(s) = symbol {
             self.model.update(s);

arithmetic-coding-core/src/model/max_length.rs

@@ -76,6 +76,14 @@ pub trait Model {
     /// The internal representation to use for storing integers
     type B: BitStore = u32;
 
+    /// The maximum denominator used for probability ranges. See
+    /// [`Model::probability`].
+    ///
+    /// This value is used to calculate an appropriate precision for the
+    /// encoding, therefore this value must not change, and
+    /// [`Model::denominator`] must never exceed it.
+    const MAX_DENOMINATOR: Self::B;
+
     /// Given a symbol, return an interval representing the probability of that
     /// symbol occurring.
     ///
@@ -107,17 +115,9 @@ pub trait Model {
     /// [`Encoder`](crate::Encoder) and [`Decoder`](crate::Decoder) to panic due
     /// to overflow or underflow.
     fn denominator(&self) -> Self::B {
-        self.max_denominator()
+        Self::MAX_DENOMINATOR
     }
 
-    /// The maximum denominator used for probability ranges. See
-    /// [`Model::probability`].
-    ///
-    /// This value is used to calculate an appropriate precision for the
-    /// encoding, therefore this value must not change, and
-    /// [`Model::denominator`] must never exceed it.
-    fn max_denominator(&self) -> Self::B;
-
     /// Given a value, return the symbol whose probability range it falls in.
     ///
     /// `None` indicates `EOF`
@@ -183,10 +183,6 @@ where
         }
     }
 
-    fn max_denominator(&self) -> Self::B {
-        self.model.max_denominator()
-    }
-
     fn symbol(&self, value: Self::B) -> Option<Self::Symbol> {
         if self.remaining > 0 {
             self.model.symbol(value)
@@ -205,6 +201,8 @@ where
             self.remaining -= 1;
         }
     }
+
+    const MAX_DENOMINATOR: Self::B = M::MAX_DENOMINATOR;
 }
 
 /// Fixed-length encoding/decoding errors

arithmetic-coding-core/src/model/one_shot.rs

@@ -69,6 +69,14 @@ pub trait Model {
     /// The internal representation to use for storing integers
     type B: BitStore = u32;
 
+    /// The maximum denominator used for probability ranges. See
+    /// [`Model::probability`].
+    ///
+    /// This value is used to calculate an appropriate precision for the
+    /// encoding, therefore this value must not change, and
+    /// [`Model::denominator`] must never exceed it.
+    const MAX_DENOMINATOR: Self::B;
+
     /// Given a symbol, return an interval representing the probability of that
     /// symbol occurring.
     ///
@@ -87,14 +95,6 @@ pub trait Model {
     /// This returns a custom error if the given symbol is not valid
     fn probability(&self, symbol: &Self::Symbol) -> Result<Range<Self::B>, Self::ValueError>;
 
-    /// The maximum denominator used for probability ranges. See
-    /// [`Model::probability`].
-    ///
-    /// This value is used to calculate an appropriate precision for the
-    /// encoding, therefore this value must not change, and
-    /// [`Model::denominator`] must never exceed it.
-    fn max_denominator(&self) -> Self::B;
-
     /// Given a value, return the symbol whose probability range it falls in.
     ///
     /// `None` indicates `EOF`
@@ -115,10 +115,6 @@ where
         Model::probability(self, symbol)
     }
 
-    fn max_denominator(&self) -> Self::B {
-        self.max_denominator()
-    }
-
     fn symbol(&self, value: Self::B) -> Self::Symbol {
         Model::symbol(self, value)
     }
@@ -128,6 +124,8 @@ where
     }
 
     fn denominator(&self) -> Self::B {
-        self.max_denominator()
+        Self::MAX_DENOMINATOR
     }
+
+    const MAX_DENOMINATOR: Self::B = Self::MAX_DENOMINATOR;
 }

benches/sherlock.rs

@@ -5,15 +5,17 @@ use fenwick_model::{simple::FenwickModel, ValueError};
 
 mod common;
 
+const MAX_DENOMINATOR: u64 = 1 << 20;
+
 #[derive(Debug, Clone)]
 pub struct StringModel {
-    fenwick_model: FenwickModel,
+    fenwick_model: FenwickModel<MAX_DENOMINATOR>,
 }
 
 impl StringModel {
     #[must_use]
     pub fn new(symbols: usize) -> Self {
-        let fenwick_model = FenwickModel::builder(symbols, 1 << 20)
+        let fenwick_model = FenwickModel::builder(symbols)
             .panic_on_saturation()
             .build();
         Self { fenwick_model }
@@ -41,13 +43,11 @@ impl Model for StringModel {
         self.fenwick_model.symbol(value).map(|x| x as u8)
     }
 
-    fn max_denominator(&self) -> Self::B {
-        self.fenwick_model.max_denominator()
-    }
-
     fn denominator(&self) -> Self::B {
         self.fenwick_model.denominator()
     }
+
+    const MAX_DENOMINATOR: Self::B = MAX_DENOMINATOR;
 }
 
 fn round_trip(input: &[u8]) {

examples/concatenated.rs

@@ -40,9 +40,7 @@ mod integer {
             }
         }
 
-        fn max_denominator(&self) -> u32 {
-            4
-        }
+        const MAX_DENOMINATOR: Self::B = 4;
     }
 }
 
@@ -81,9 +79,7 @@ mod symbolic {
             }
         }
 
-        fn max_denominator(&self) -> u32 {
-            4
-        }
+        const MAX_DENOMINATOR: Self::B = 4;
     }
 }
 

examples/fenwick_adaptive.rs

@@ -9,16 +9,18 @@ use fenwick_model::{simple::FenwickModel, ValueError};
 const ALPHABET: &str =
     "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789 .,\n-':()[]#*;\"!?*&é/àâè%@$";
 
+const MAX_DENOMINATOR: u64 = 1 << 20;
+
 #[derive(Debug, Clone)]
 pub struct StringModel {
     alphabet: Vec<char>,
-    fenwick_model: FenwickModel,
+    fenwick_model: FenwickModel<MAX_DENOMINATOR>,
 }
 
 impl StringModel {
     #[must_use]
     pub fn new(alphabet: Vec<char>) -> Self {
-        let fenwick_model = FenwickModel::builder(alphabet.len(), 1 << 20)
+        let fenwick_model = FenwickModel::builder(alphabet.len())
             .panic_on_saturation()
             .build();
         Self {
@@ -50,10 +52,6 @@ impl Model for StringModel {
         self.alphabet.get(index).copied()
     }
 
-    fn max_denominator(&self) -> Self::B {
-        self.fenwick_model.max_denominator()
-    }
-
     fn denominator(&self) -> Self::B {
         self.fenwick_model.denominator()
     }
@@ -62,6 +60,8 @@ impl Model for StringModel {
         let fenwick_symbol = symbol.map(|c| self.alphabet.iter().position(|x| x == c).unwrap());
         self.fenwick_model.update(fenwick_symbol.as_ref());
     }
+
+    const MAX_DENOMINATOR: Self::B = MAX_DENOMINATOR;
 }
 
 fn main() {

examples/fenwick_context_switching.rs

@@ -9,16 +9,18 @@ use fenwick_model::{context_switching::FenwickModel, ValueError};
 const ALPHABET: &str =
     "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789 .,\n-':()[]#*;\"!?*&é/àâè%@$";
 
+const MAX_DENOMINATOR: u64 = 1 << 17;
+
 #[derive(Debug, Clone)]
 pub struct StringModel {
     alphabet: Vec<char>,
-    fenwick_model: FenwickModel,
+    fenwick_model: FenwickModel<MAX_DENOMINATOR>,
 }
 
 impl StringModel {
     #[must_use]
     pub fn new(alphabet: Vec<char>) -> Self {
-        let fenwick_model = FenwickModel::with_symbols(alphabet.len(), 1 << 17);
+        let fenwick_model = FenwickModel::with_symbols(alphabet.len());
         Self {
             alphabet,
             fenwick_model,
@@ -48,10 +50,6 @@ impl Model for StringModel {
         self.alphabet.get(index).copied()
     }
 
-    fn max_denominator(&self) -> Self::B {
-        self.fenwick_model.max_denominator()
-    }
-
     fn denominator(&self) -> Self::B {
         self.fenwick_model.denominator()
     }
@@ -60,6 +58,8 @@ impl Model for StringModel {
         let fenwick_symbol = symbol.map(|c| self.alphabet.iter().position(|x| x == c).unwrap());
         self.fenwick_model.update(fenwick_symbol.as_ref());
     }
+
+    const MAX_DENOMINATOR: Self::B = MAX_DENOMINATOR;
 }
 
 fn main() {

examples/fixed_length.rs

@@ -38,13 +38,11 @@ impl fixed_length::Model for MyModel {
         }
     }
 
-    fn max_denominator(&self) -> u32 {
-        3
-    }
-
     fn length(&self) -> usize {
         3
     }
+
+    const MAX_DENOMINATOR: Self::B = 3;
 }
 
 fn main() {

examples/integer.rs

@@ -37,9 +37,7 @@ impl Model for MyModel {
         }
     }
 
-    fn max_denominator(&self) -> u32 {
-        4
-    }
+    const MAX_DENOMINATOR: Self::B = 4;
 }
 
 fn main() {

examples/max_length.rs

@@ -40,13 +40,13 @@ impl max_length::Model for MyModel {
         }
     }
 
-    fn max_denominator(&self) -> u32 {
-        4
-    }
-
     fn max_length(&self) -> usize {
         3
     }
+
+    type B = u32;
+
+    const MAX_DENOMINATOR: Self::B = 4;
 }
 
 fn main() {