add OpsIdentity trait

Author: ChihChengLiang

eth-types/src/lib.rs

@@ -24,9 +24,12 @@ pub use keccak::{keccak256, Keccak};
 
 pub use bytecode::Bytecode;
 pub use error::Error;
-use halo2_proofs::halo2curves::{
-    bn256::{Fq, Fr},
-    ff::{Field as Halo2Field, FromUniformBytes, PrimeField},
+use halo2_proofs::{
+    halo2curves::{
+        bn256::{Fq, Fr},
+        ff::{Field as Halo2Field, FromUniformBytes, PrimeField},
+    },
+    plonk::Expression,
 };
 
 use crate::evm_types::{memory::Memory, stack::Stack, storage::Storage, OpcodeId};
@@ -42,9 +45,58 @@ pub use ethers_core::{
 use serde::{de, Deserialize, Serialize};
 use std::{collections::HashMap, fmt, str::FromStr};
 
+/// trait to retrieve general operation itentity element
+pub trait OpsIdentity {
+    /// output type
+    type Output;
+    /// additive identity
+    fn zero() -> Self::Output;
+    /// multiplicative identity
+    fn one() -> Self::Output;
+}
+
+impl<F: Field> OpsIdentity for Expression<F> {
+    type Output = Expression<F>;
+    fn zero() -> Self::Output {
+        Expression::Constant(F::ZERO)
+    }
+
+    fn one() -> Self::Output {
+        Expression::Constant(F::ONE)
+    }
+}
+
+// Impl OpsIdentity for Fr
+impl OpsIdentity for Fr {
+    type Output = Fr;
+
+    fn zero() -> Self::Output {
+        Fr::zero()
+    }
+
+    fn one() -> Self::Output {
+        Fr::one()
+    }
+}
+
+// Impl OpsIdentity for Fq
+impl OpsIdentity for Fq {
+    type Output = Fq;
+
+    fn zero() -> Self::Output {
+        Fq::zero()
+    }
+
+    fn one() -> Self::Output {
+        Fq::one()
+    }
+}
+
 /// Trait used to reduce verbosity with the declaration of the [`PrimeField`]
 /// trait and its repr.
-pub trait Field: Halo2Field + PrimeField<Repr = [u8; 32]> + FromUniformBytes<64> + Ord {
+pub trait Field:
+    Halo2Field + PrimeField<Repr = [u8; 32]> + FromUniformBytes<64> + Ord + OpsIdentity<Output = Self>
+{
     /// Gets the lower 128 bits of this field element when expressed
     /// canonically.
     fn get_lower_128(&self) -> u128 {

zkevm-circuits/src/util/word.rs

@@ -4,7 +4,7 @@
 //   limb is 256/4 = 64 bits
 
 use bus_mapping::state_db::CodeDB;
-use eth_types::{Field, ToLittleEndian, H160, H256};
+use eth_types::{Field, OpsIdentity, ToLittleEndian, H160, H256};
 use gadgets::util::{not, or, Expr};
 use halo2_proofs::{
     circuit::{AssignedCell, Region, Value},
@@ -267,6 +267,17 @@ impl<F: Field> From<eth_types::Word> for Word<F> {
     }
 }
 
+impl<T: Clone + OpsIdentity<Output = T>> OpsIdentity for Word<T> {
+    /// output type
+    type Output = Word<T>;
+    fn zero() -> Self::Output {
+        Word::new([T::zero(), T::zero()])
+    }
+    fn one() -> Self::Output {
+        Word::new([T::one(), T::zero()])
+    }
+}
+
 impl<F: Field> From<H256> for Word<F> {
     /// Construct the word from H256
     fn from(h: H256) -> Self {
@@ -354,16 +365,6 @@ impl<F: Field, T: Expr<F> + Clone> WordExpr<F> for Word<T> {
 }
 
 impl<F: Field> Word<F> {
-    /// zero word
-    pub fn zero_f() -> Self {
-        Self::new([F::ZERO, F::ZERO])
-    }
-
-    /// one word
-    pub fn one_f() -> Self {
-        Self::new([F::ONE, F::ZERO])
-    }
-
     /// Convert address (h160) to single field element.
     /// This method is Address specific
     pub fn compress_f(&self) -> F {
@@ -376,15 +377,6 @@ impl<F: Field> Word<Expression<F>> {
     pub fn from_lo_unchecked(lo: Expression<F>) -> Self {
         Self::new([lo, 0.expr()])
     }
-    /// zero word
-    pub fn zero() -> Self {
-        Self::new([0.expr(), 0.expr()])
-    }
-
-    /// one word
-    pub fn one() -> Self {
-        Self::new([1.expr(), 0.expr()])
-    }
 
     /// select based on selector. Here assume selector is 1/0 therefore no overflow check
     pub fn select<T: Expr<F> + Clone>(