From fd6b971d221ddfdf2e57fc25d0ff35bb465e65ef Mon Sep 17 00:00:00 2001
From: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
Date: Wed, 15 Mar 2023 21:43:22 +0100
Subject: [PATCH] Add dedicated `FeePolynomial` struct (#13612)
* Add FeePolynomial struct
Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
* Add Weight::without_{ref_time, proof_size}
Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
* Docs
Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
* Cleanup code
Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
* Add docs
Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
* doc
Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
* Fix docs
Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
* docs
Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
---------
Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
---
substrate/primitives/weights/src/lib.rs | 95 ++++++++++++++-----
substrate/primitives/weights/src/weight_v2.rs | 10 ++
2 files changed, 82 insertions(+), 23 deletions(-)
diff --git a/substrate/primitives/weights/src/lib.rs b/substrate/primitives/weights/src/lib.rs
index 8a842307355..faa641a0f0c 100644
--- a/substrate/primitives/weights/src/lib.rs
+++ b/substrate/primitives/weights/src/lib.rs
@@ -30,7 +30,7 @@ use scale_info::TypeInfo;
use serde::{Deserialize, Serialize};
use smallvec::SmallVec;
use sp_arithmetic::{
- traits::{BaseArithmetic, SaturatedConversion, Saturating, Unsigned},
+ traits::{BaseArithmetic, SaturatedConversion, Unsigned},
Perbill,
};
use sp_core::Get;
@@ -118,9 +118,77 @@ pub struct WeightToFeeCoefficient<Balance> {
pub degree: u8,
}
-/// A list of coefficients that represent one polynomial.
+impl<Balance> WeightToFeeCoefficient<Balance>
+where
+ Balance: BaseArithmetic + From<u32> + Copy + Unsigned,
+{
+ /// Evaluate the term at `x` and saturatingly amalgamate into `result`.
+ ///
+ /// The unsigned value for the term is calculated as:
+ /// ```ignore
+ /// (frac * x^(degree) + integer * x^(degree))
+ /// ```
+ /// Depending on the value of `negative`, it is added or subtracted from the `result`.
+ pub fn saturating_eval(&self, mut result: Balance, x: Balance) -> Balance {
+ let power = x.saturating_pow(self.degree.into());
+
+ let frac = self.coeff_frac * power; // Overflow safe.
+ let integer = self.coeff_integer.saturating_mul(power);
+ // Do not add them together here to avoid an underflow.
+
+ if self.negative {
+ result = result.saturating_sub(frac);
+ result = result.saturating_sub(integer);
+ } else {
+ result = result.saturating_add(frac);
+ result = result.saturating_add(integer);
+ }
+
+ result
+ }
+}
+
+/// A list of coefficients that represent a polynomial.
pub type WeightToFeeCoefficients<T> = SmallVec<[WeightToFeeCoefficient<T>; 4]>;
+/// A list of coefficients that represent a polynomial.
+///
+/// Can be [eval](Self::eval)uated at a specific `u64` to get the fee. The evaluations happens by
+/// summing up all term [results](`WeightToFeeCoefficient::saturating_eval`). The order of the
+/// coefficients matters since it uses saturating arithmetic. This struct does therefore not model a
+/// polynomial in the mathematical sense (polynomial ring).
+///
+/// For visualization purposes, the formulas of the unsigned terms look like:
+///
+/// ```ignore
+/// (c[0].frac * x^(c[0].degree) + c[0].integer * x^(c[0].degree))
+/// (c[1].frac * x^(c[1].degree) + c[1].integer * x^(c[1].degree))
+/// ...
+/// ```
+/// Depending on the value of `c[i].negative`, each term is added or subtracted from the result.
+/// The result is initialized as zero.
+pub struct FeePolynomial<Balance> {
+ coefficients: SmallVec<[WeightToFeeCoefficient<Balance>; 4]>,
+}
+
+impl<Balance> From<WeightToFeeCoefficients<Balance>> for FeePolynomial<Balance> {
+ fn from(coefficients: WeightToFeeCoefficients<Balance>) -> Self {
+ Self { coefficients }
+ }
+}
+
+impl<Balance> FeePolynomial<Balance>
+where
+ Balance: BaseArithmetic + From<u32> + Copy + Unsigned,
+{
+ /// Evaluate the polynomial at a specific `x`.
+ pub fn eval(&self, x: u64) -> Balance {
+ self.coefficients.iter().fold(Balance::zero(), |acc, term| {
+ term.saturating_eval(acc, Balance::saturated_from(x))
+ })
+ }
+}
+
/// A trait that describes the weight to fee calculation.
pub trait WeightToFee {
/// The type that is returned as result from calculation.
@@ -157,27 +225,8 @@ where
/// This should not be overridden in most circumstances. Calculation is done in the
/// `Balance` type and never overflows. All evaluation is saturating.
fn weight_to_fee(weight: &Weight) -> Self::Balance {
- Self::polynomial()
- .iter()
- .fold(Self::Balance::saturated_from(0u32), |mut acc, args| {
- let w = Self::Balance::saturated_from(weight.ref_time())
- .saturating_pow(args.degree.into());
-
- // The sum could get negative. Therefore we only sum with the accumulator.
- // The Perbill Mul implementation is non overflowing.
- let frac = args.coeff_frac * w;
- let integer = args.coeff_integer.saturating_mul(w);
-
- if args.negative {
- acc = acc.saturating_sub(frac);
- acc = acc.saturating_sub(integer);
- } else {
- acc = acc.saturating_add(frac);
- acc = acc.saturating_add(integer);
- }
-
- acc
- })
+ let poly: FeePolynomial<Self::Balance> = Self::polynomial().into();
+ poly.eval(weight.ref_time())
}
}
diff --git a/substrate/primitives/weights/src/weight_v2.rs b/substrate/primitives/weights/src/weight_v2.rs
index ca137145920..76c40c16cbf 100644
--- a/substrate/primitives/weights/src/weight_v2.rs
+++ b/substrate/primitives/weights/src/weight_v2.rs
@@ -74,6 +74,16 @@ impl Weight {
&mut self.proof_size
}
+ /// Return self but discard any reference time.
+ pub const fn without_ref_time(&self) -> Self {
+ Self { ref_time: 0, proof_size: self.proof_size }
+ }
+
+ /// Return self but discard any proof size.
+ pub const fn without_proof_size(&self) -> Self {
+ Self { ref_time: self.ref_time, proof_size: 0 }
+ }
+
pub const MAX: Self = Self { ref_time: u64::MAX, proof_size: u64::MAX };
/// Get the conservative min of `self` and `other` weight.
--
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