add optimization comment

scroll-tech · Jun 27, 2024 · d0e1d06 · d0e1d06
1 parent ca607d2
commit d0e1d06
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Showing 2 changed files with 8 additions and 7 deletions.
diff --git a/singer-utils/src/uint/constants.rs b/singer-utils/src/uint/constants.rs
@@ -57,9 +57,10 @@ impl<const M: usize, const C: usize> AddSubConstants<UInt<M, C>> {
 
     pub const N_NO_OVERFLOW_WITNESS_UNSAFE_CELLS: usize = Self::N_CARRY_CELLS_NO_OVERFLOW;
 
-    // /// The number of `RANGE_CHIP_BIT_WIDTH` cells needed to represent the carry cells, assuming
-    // /// no overflow.
-    // pub const N_RANGE_CELLS_IN_CARRY_NO_OVERFLOW: usize =
-    //     Self::N_CARRY_CELLS_NO_OVERFLOW * UInt::<M, C>::N_RANGE_CELLS_PER_CELL;
-
+    /// The number of `RANGE_CHIP_BIT_WIDTH` cells needed to represent the carry cells, assuming
+    /// no overflow.
+    // TODO: if guaranteed no overflow, then we don't need to range check the highest limb
+    //  hence this can be (N_OPERANDS - 1) * N_RANGE_CELLS_PER_CELL
+    //  update this once, range check logic doesn't assume all limbs
+    pub const N_RANGE_CELLS_IN_CARRY_NO_OVERFLOW: usize = UInt::<M, C>::N_RANGE_CELLS;
 }
diff --git a/singer-utils/src/uint/witness_extractors.rs b/singer-utils/src/uint/witness_extractors.rs
@@ -11,7 +11,7 @@ impl<const M: usize, const C: usize> UInt<M, C> {
     }
 
     pub fn extract_carry_no_overflow(witness: &[CellId]) -> &[CellId] {
-        &witness[Self::N_RANGE_CELLS..]
+        &witness[AddSubConstants::<Self>::N_RANGE_CELLS_IN_CARRY_NO_OVERFLOW..]
     }
 
     // TODO: why do we need this
@@ -33,6 +33,6 @@ impl<const M: usize, const C: usize> UInt<M, C> {
     }
 
     pub fn extract_range_values_no_overflow(witness: &[CellId]) -> &[CellId] {
-        &witness[..Self::N_RANGE_CELLS]
+        &witness[..AddSubConstants::<Self>::N_RANGE_CELLS_IN_CARRY_NO_OVERFLOW]
     }
 }