Recognise UInt::from_exprs_unchecked can't fail (#486)

Extracted from #466 and addressing https://github.com/scroll-tech/ceno/pull/455/files#r1818907561
scroll-tech · Oct 28, 2024 · 81b5745 · 81b5745
1 parent e949246
commit 81b5745
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Showing 7 changed files with 16 additions and 24 deletions.
diff --git a/ceno_zkvm/src/gadgets/signed_ext.rs b/ceno_zkvm/src/gadgets/signed_ext.rs
@@ -68,9 +68,7 @@ impl SignedExtendConfig {
             16 => val,
             _ => unreachable!("unsupported N_BITS = {}", self.n_bits),
         };
-
-        // it's safe to unwrap as `UInt::from_exprs_unchecked` never return error
-        UInt::from_exprs_unchecked(vec![limb0, self.msb.expr() * 0xffff]).unwrap()
+        UInt::from_exprs_unchecked(vec![limb0, self.msb.expr() * 0xffff])
     }
 
     pub fn assign_instance<E: ExtensionField>(

diff --git a/ceno_zkvm/src/instructions/riscv/memory/load.rs b/ceno_zkvm/src/instructions/riscv/memory/load.rs
@@ -155,8 +155,7 @@ impl<E: ExtensionField, I: RIVInstruction> Instruction<E> for LoadInstruction<E,
                     UInt::from_exprs_unchecked(vec![
                         target_limb.as_ref().map(|limb| limb.expr()).unwrap(),
                         Expression::ZERO,
-                    ])
-                    .unwrap(),
+                    ]),
                 )
             }
             InsnKind::LB => {
@@ -167,14 +166,10 @@ impl<E: ExtensionField, I: RIVInstruction> Instruction<E> for LoadInstruction<E,
 
                 (Some(signed_extend_config), rd_written)
             }
-            InsnKind::LBU => {
-                (
-                    None,
-                    // it's safe to unwrap as `UInt::from_exprs_unchecked` never return error
-                    UInt::from_exprs_unchecked(vec![target_byte_expr.unwrap(), Expression::ZERO])
-                        .unwrap(),
-                )
-            }
+            InsnKind::LBU => (
+                None,
+                UInt::from_exprs_unchecked(vec![target_byte_expr.unwrap(), Expression::ZERO]),
+            ),
             _ => unreachable!("Unsupported instruction kind {:?}", I::INST_KIND),
         };
 

diff --git a/ceno_zkvm/src/instructions/riscv/slt.rs b/ceno_zkvm/src/instructions/riscv/slt.rs
@@ -39,7 +39,7 @@ impl<E: ExtensionField> Instruction<E> for SltInstruction<E> {
         let rs2_read = UInt::new_unchecked(|| "rs2_read", cb)?;
 
         let lt = SignedLtConfig::construct_circuit(cb, || "rs1 < rs2", &rs1_read, &rs2_read)?;
-        let rd_written = UInt::from_exprs_unchecked(vec![lt.expr()])?;
+        let rd_written = UInt::from_exprs_unchecked(vec![lt.expr()]);
 
         let r_insn = RInstructionConfig::<E>::construct_circuit(
             cb,

diff --git a/ceno_zkvm/src/instructions/riscv/slti.rs b/ceno_zkvm/src/instructions/riscv/slti.rs
@@ -63,7 +63,7 @@ impl<E: ExtensionField> Instruction<E> for SltiInstruction<E> {
             imm.expr(),
             UINT_LIMBS,
         )?;
-        let rd_written = UInt::from_exprs_unchecked(vec![lt.expr()])?;
+        let rd_written = UInt::from_exprs_unchecked(vec![lt.expr()]);
 
         let i_insn = IInstructionConfig::<E>::construct_circuit(
             cb,

diff --git a/ceno_zkvm/src/instructions/riscv/sltu.rs b/ceno_zkvm/src/instructions/riscv/sltu.rs
@@ -57,7 +57,7 @@ impl<E: ExtensionField, I: RIVInstruction> Instruction<E> for ArithInstruction<E
             rs2_read.value(),
             UINT_LIMBS,
         )?;
-        let rd_written = UInt::from_exprs_unchecked(vec![lt.expr()])?;
+        let rd_written = UInt::from_exprs_unchecked(vec![lt.expr()]);
 
         let r_insn = RInstructionConfig::<E>::construct_circuit(
             circuit_builder,

diff --git a/ceno_zkvm/src/uint.rs b/ceno_zkvm/src/uint.rs
@@ -302,7 +302,7 @@ impl<const M: usize, const C: usize, E: ExtensionField> UIntLimbs<M, C, E> {
                     .unwrap()
             })
             .collect_vec();
-        UIntLimbs::<M, C, E>::from_exprs_unchecked(combined_limbs)
+        Ok(UIntLimbs::<M, C, E>::from_exprs_unchecked(combined_limbs))
     }
 
     pub fn to_u8_limbs(
@@ -345,8 +345,8 @@ impl<const M: usize, const C: usize, E: ExtensionField> UIntLimbs<M, C, E> {
         UIntLimbs::<M, 8, E>::create_witin_from_exprs(circuit_builder, split_limbs)
     }
 
-    pub fn from_exprs_unchecked(expr_limbs: Vec<Expression<E>>) -> Result<Self, ZKVMError> {
-        let n = Self {
+    pub fn from_exprs_unchecked(expr_limbs: Vec<Expression<E>>) -> Self {
+        Self {
             limbs: UintLimb::Expression(
                 expr_limbs
                     .into_iter()
@@ -356,8 +356,7 @@ impl<const M: usize, const C: usize, E: ExtensionField> UIntLimbs<M, C, E> {
             ),
             carries: None,
             carries_auxiliary_lt_config: None,
-        };
-        Ok(n)
+        }
     }
 
     /// If current limbs are Expression, this function will create witIn and replace the limbs
@@ -523,8 +522,8 @@ impl<const M: usize, const C: usize, E: ExtensionField> UIntLimbs<M, C, E> {
         let mut self_lo = self.expr();
         let self_hi = self_lo.split_off(self_lo.len() / 2);
         Ok((
-            UIntLimbs::from_exprs_unchecked(self_lo)?,
-            UIntLimbs::from_exprs_unchecked(self_hi)?,
+            UIntLimbs::from_exprs_unchecked(self_lo),
+            UIntLimbs::from_exprs_unchecked(self_hi),
         ))
     }
 

diff --git a/ceno_zkvm/src/uint/arithmetic.rs b/ceno_zkvm/src/uint/arithmetic.rs
@@ -241,7 +241,7 @@ impl<const M: usize, const C: usize, E: ExtensionField> UIntLimbs<M, C, E> {
                 mul_hi
             } else {
                 // lo limb
-                UIntLimbs::from_exprs_unchecked(mul.expr())?
+                UIntLimbs::from_exprs_unchecked(mul.expr())
             };
             let add = cb.namespace(
                 || "add",