chore!: Add a low and high limb to scalar mul opcode (#532)

acir/src/circuit/opcodes/black_box_function_call.rs

@@ -72,7 +72,8 @@ pub enum BlackBoxFuncCall {
         output: Witness,
     },
     FixedBaseScalarMul {
-        input: FunctionInput,
+        low: FunctionInput,
+        high: FunctionInput,
         outputs: (Witness, Witness),
     },
     Keccak256 {
@@ -160,7 +161,8 @@ impl BlackBoxFuncCall {
                 output: Witness(0),
             },
             BlackBoxFunc::FixedBaseScalarMul => BlackBoxFuncCall::FixedBaseScalarMul {
-                input: FunctionInput::dummy(),
+                low: FunctionInput::dummy(),
+                high: FunctionInput::dummy(),
                 outputs: (Witness(0), Witness(0)),
             },
             BlackBoxFunc::Keccak256 => {
@@ -210,8 +212,8 @@ impl BlackBoxFuncCall {
             BlackBoxFuncCall::AND { lhs, rhs, .. } | BlackBoxFuncCall::XOR { lhs, rhs, .. } => {
                 vec![*lhs, *rhs]
             }
-            BlackBoxFuncCall::FixedBaseScalarMul { input, .. }
-            | BlackBoxFuncCall::RANGE { input } => vec![*input],
+            BlackBoxFuncCall::FixedBaseScalarMul { low, high, .. } => vec![*low, *high],
+            BlackBoxFuncCall::RANGE { input } => vec![*input],
             BlackBoxFuncCall::SchnorrVerify {
                 public_key_x,
                 public_key_y,

acir/tests/test_program_serialization.rs

@@ -60,7 +60,8 @@ fn addition_circuit() {
 #[test]
 fn fixed_base_scalar_mul_circuit() {
     let fixed_base_scalar_mul = Opcode::BlackBoxFuncCall(BlackBoxFuncCall::FixedBaseScalarMul {
-        input: FunctionInput { witness: Witness(1), num_bits: FieldElement::max_num_bits() },
+        low: FunctionInput { witness: Witness(1), num_bits: FieldElement::max_num_bits() },
+        high: FunctionInput { witness: Witness(1), num_bits: FieldElement::max_num_bits() },
         outputs: (Witness(2), Witness(3)),
     });
 
@@ -76,9 +77,9 @@ fn fixed_base_scalar_mul_circuit() {
     circuit.write(&mut bytes).unwrap();
 
     let expected_serialization: Vec<u8> = vec![
-        31, 139, 8, 0, 0, 0, 0, 0, 0, 255, 93, 137, 91, 10, 0, 0, 4, 4, 215, 227, 203, 253, 207,
-        43, 132, 146, 169, 105, 106, 87, 1, 16, 154, 170, 77, 61, 229, 84, 222, 191, 240, 169, 156,
-        61, 0, 36, 111, 164, 5, 80, 0, 0, 0,
+        31, 139, 8, 0, 0, 0, 0, 0, 0, 255, 93, 202, 65, 10, 0, 64, 8, 2, 64, 183, 246, 212, 255,
+        223, 27, 21, 21, 72, 130, 12, 136, 31, 192, 67, 167, 180, 209, 73, 201, 234, 249, 109, 132,
+        84, 218, 3, 23, 46, 165, 61, 88, 0, 0, 0,
     ];
 
     assert_eq!(bytes, expected_serialization)

acvm/src/pwg/blackbox/fixed_base_scalar_mul.rs

@@ -11,12 +11,14 @@ use crate::{
 pub(super) fn fixed_base_scalar_mul(
     backend: &impl BlackBoxFunctionSolver,
     initial_witness: &mut WitnessMap,
-    input: FunctionInput,
+    low: FunctionInput,
+    high: FunctionInput,
     outputs: (Witness, Witness),
 ) -> Result<(), OpcodeResolutionError> {
-    let scalar = witness_to_value(initial_witness, input.witness)?;
+    let low = witness_to_value(initial_witness, low.witness)?;
+    let high = witness_to_value(initial_witness, high.witness)?;
 
-    let (pub_x, pub_y) = backend.fixed_base_scalar_mul(scalar)?;
+    let (pub_x, pub_y) = backend.fixed_base_scalar_mul(low, high)?;
 
     insert_value(&outputs.0, pub_x, initial_witness)?;
     insert_value(&outputs.1, pub_y, initial_witness)?;

acvm/src/pwg/blackbox/mod.rs

@@ -148,8 +148,8 @@ pub(crate) fn solve(
             message,
             *output,
         ),
-        BlackBoxFuncCall::FixedBaseScalarMul { input, outputs } => {
-            fixed_base_scalar_mul(backend, initial_witness, *input, *outputs)
+        BlackBoxFuncCall::FixedBaseScalarMul { low, high, outputs } => {
+            fixed_base_scalar_mul(backend, initial_witness, *low, *high, *outputs)
         }
         BlackBoxFuncCall::RecursiveAggregation { output_aggregation_object, .. } => {
             // Solve the output of the recursive aggregation to zero to prevent missing assignment errors

acvm/tests/solver.rs

@@ -38,7 +38,8 @@ impl BlackBoxFunctionSolver for StubbedBackend {
     }
     fn fixed_base_scalar_mul(
         &self,
-        _input: &FieldElement,
+        _low: &FieldElement,
+        _high: &FieldElement,
     ) -> Result<(FieldElement, FieldElement), BlackBoxResolutionError> {
         panic!("Path not trodden by this test")
     }

acvm_js/test/shared/fixed_base_scalar_mul.ts

@@ -1,10 +1,9 @@
 // See `fixed_base_scalar_mul_circuit` integration test in `acir/tests/test_program_serialization.rs`.
 export const bytecode = Uint8Array.from([
-  31, 139, 8, 0, 0, 0, 0, 0, 0, 255, 93, 137, 91, 10, 0, 0, 4, 4, 215, 227, 203,
-  253, 207, 43, 132, 146, 169, 105, 106, 87, 1, 16, 154, 170, 77, 61, 229, 84,
-  222, 191, 240, 169, 156, 61, 0, 36, 111, 164, 5, 80, 0, 0, 0,
+  31, 139, 8, 0, 0, 0, 0, 0, 0, 255, 93, 202, 65, 10, 0, 64, 8, 2, 64, 183, 246,
+  212, 255, 223, 27, 21, 21, 72, 130, 12, 136, 31, 192, 67, 167, 180, 209, 73,
+  201, 234, 249, 109, 132, 84, 218, 3, 23, 46, 165, 61, 88, 0, 0, 0,
 ]);
-
 export const initialWitnessMap = new Map([
   [1, "0x0000000000000000000000000000000000000000000000000000000000000001"],
 ]);

blackbox_solver/src/barretenberg/mod.rs

@@ -71,10 +71,11 @@ impl BlackBoxFunctionSolver for BarretenbergSolver {
 
     fn fixed_base_scalar_mul(
         &self,
-        input: &FieldElement,
+        low: &FieldElement,
+        high: &FieldElement,
     ) -> Result<(FieldElement, FieldElement), BlackBoxResolutionError> {
         #[allow(deprecated)]
-        self.blackbox_vendor.fixed_base(input).map_err(|err| {
+        self.blackbox_vendor.fixed_base(low, high).map_err(|err| {
             BlackBoxResolutionError::Failed(BlackBoxFunc::FixedBaseScalarMul, err.to_string())
         })
     }

blackbox_solver/src/barretenberg/wasm/scalar_mul.rs

@@ -3,14 +3,22 @@ use acir::FieldElement;
 use super::{Barretenberg, Error, FIELD_BYTES};
 
 pub(crate) trait ScalarMul {
-    fn fixed_base(&self, input: &FieldElement) -> Result<(FieldElement, FieldElement), Error>;
+    fn fixed_base(
+        &self,
+        low: &FieldElement,
+        high: &FieldElement,
+    ) -> Result<(FieldElement, FieldElement), Error>;
 }
 
 impl ScalarMul for Barretenberg {
-    fn fixed_base(&self, input: &FieldElement) -> Result<(FieldElement, FieldElement), Error> {
+    fn fixed_base(
+        &self,
+        low: &FieldElement,
+        _high: &FieldElement,
+    ) -> Result<(FieldElement, FieldElement), Error> {
         let lhs_ptr: usize = 0;
         let result_ptr: usize = lhs_ptr + FIELD_BYTES;
-        self.transfer_to_heap(&input.to_be_bytes(), lhs_ptr);
+        self.transfer_to_heap(&low.to_be_bytes(), lhs_ptr);
 
         self.call_multiple("compute_public_key", vec![&lhs_ptr.into(), &result_ptr.into()])?;
 
@@ -34,7 +42,7 @@ mod test {
         let barretenberg = Barretenberg::new();
         let input = FieldElement::one();
 
-        let res = barretenberg.fixed_base(&input)?;
+        let res = barretenberg.fixed_base(&input, &FieldElement::zero())?;
         let x = "0000000000000000000000000000000000000000000000000000000000000001";
         let y = "0000000000000002cf135e7506a45d632d270d45f1181294833fc48d823f272c";
 

blackbox_solver/src/lib.rs

@@ -44,7 +44,8 @@ pub trait BlackBoxFunctionSolver {
     ) -> Result<(FieldElement, FieldElement), BlackBoxResolutionError>;
     fn fixed_base_scalar_mul(
         &self,
-        input: &FieldElement,
+        low: &FieldElement,
+        high: &FieldElement,
     ) -> Result<(FieldElement, FieldElement), BlackBoxResolutionError>;
 }
 

brillig/src/black_box.rs

@@ -43,6 +43,6 @@ pub enum BlackBoxOp {
     },
     /// Calculates a Pedersen commitment to the inputs.
     Pedersen { inputs: HeapVector, domain_separator: RegisterIndex, output: HeapArray },
-    /// Performs scalar multiplication over the embedded curve on which [`FieldElement`][acir_field::FieldElement] is defined.
-    FixedBaseScalarMul { input: RegisterIndex, result: HeapArray },
+    /// Performs scalar multiplication over the embedded curve.
+    FixedBaseScalarMul { low: RegisterIndex, high: RegisterIndex, result: HeapArray },
 }

brillig_vm/src/black_box.rs

@@ -140,9 +140,10 @@ pub(crate) fn evaluate_black_box<Solver: BlackBoxFunctionSolver>(
             registers.set(*result, verified.into());
             Ok(())
         }
-        BlackBoxOp::FixedBaseScalarMul { input, result } => {
-            let input = registers.get(*input).to_field();
-            let (x, y) = solver.fixed_base_scalar_mul(&input)?;
+        BlackBoxOp::FixedBaseScalarMul { low, high, result } => {
+            let low = registers.get(*low).to_field();
+            let high = registers.get(*high).to_field();
+            let (x, y) = solver.fixed_base_scalar_mul(&low, &high)?;
             memory.write_slice(registers.get(result.pointer).to_usize(), &[x.into(), y.into()]);
             Ok(())
         }

brillig_vm/src/lib.rs

@@ -410,7 +410,8 @@ impl BlackBoxFunctionSolver for DummyBlackBoxSolver {
     }
     fn fixed_base_scalar_mul(
         &self,
-        _input: &FieldElement,
+        _low: &FieldElement,
+        _high: &FieldElement,
     ) -> Result<(FieldElement, FieldElement), BlackBoxResolutionError> {
         Ok((4_u128.into(), 5_u128.into()))
     }