chore(acvm)!: expose separate solvers for AND and XOR opcodes (#266)

* chore!: expose separate solvers for AND and XOR opcodes

* chore: replace boolean flag and `num_bits` args with closure

Author: TomAFrench

acvm/src/pwg/logic.rs

@@ -1,58 +1,28 @@
 use super::{insert_value, witness_to_value};
 use crate::{pwg::OpcodeResolution, OpcodeResolutionError};
-use acir::{circuit::opcodes::BlackBoxFuncCall, native_types::Witness, BlackBoxFunc, FieldElement};
+use acir::{circuit::opcodes::BlackBoxFuncCall, native_types::Witness, FieldElement};
 use std::collections::BTreeMap;
 
-pub fn solve_logic_opcode(
+/// Solves a [`BlackBoxFunc::And`][acir::circuit::black_box_functions::BlackBoxFunc::AND] opcode and inserts
+/// the result into the supplied witness map
+pub fn and(
     initial_witness: &mut BTreeMap<Witness, FieldElement>,
-    func_call: &BlackBoxFuncCall,
+    gate: &BlackBoxFuncCall,
 ) -> Result<OpcodeResolution, OpcodeResolutionError> {
-    match func_call.name {
-        BlackBoxFunc::AND => LogicSolver::solve_and_gate(initial_witness, func_call),
-        BlackBoxFunc::XOR => LogicSolver::solve_xor_gate(initial_witness, func_call),
-        _ => Err(OpcodeResolutionError::UnexpectedOpcode("logic opcode", func_call.name)),
-    }
+    let (a, b, result, num_bits) = extract_input_output(gate);
+    solve_logic_gate(initial_witness, &a, &b, result, |left, right| left.and(right, num_bits))
 }
 
-pub struct LogicSolver;
-
-impl LogicSolver {
-    /// Derives the rest of the witness based on the initial low level variables
-    fn solve_logic_gate(
-        initial_witness: &mut BTreeMap<Witness, FieldElement>,
-        a: &Witness,
-        b: &Witness,
-        result: Witness,
-        num_bits: u32,
-        is_xor_gate: bool,
-    ) -> Result<OpcodeResolution, OpcodeResolutionError> {
-        let w_l_value = witness_to_value(initial_witness, *a)?;
-        let w_r_value = witness_to_value(initial_witness, *b)?;
-
-        let assignment = if is_xor_gate {
-            w_l_value.xor(w_r_value, num_bits)
-        } else {
-            w_l_value.and(w_r_value, num_bits)
-        };
-        insert_value(&result, assignment, initial_witness)?;
-        Ok(OpcodeResolution::Solved)
-    }
-
-    pub fn solve_and_gate(
-        initial_witness: &mut BTreeMap<Witness, FieldElement>,
-        gate: &BlackBoxFuncCall,
-    ) -> Result<OpcodeResolution, OpcodeResolutionError> {
-        let (a, b, result, num_bits) = extract_input_output(gate);
-        LogicSolver::solve_logic_gate(initial_witness, &a, &b, result, num_bits, false)
-    }
-    pub fn solve_xor_gate(
-        initial_witness: &mut BTreeMap<Witness, FieldElement>,
-        gate: &BlackBoxFuncCall,
-    ) -> Result<OpcodeResolution, OpcodeResolutionError> {
-        let (a, b, result, num_bits) = extract_input_output(gate);
-        LogicSolver::solve_logic_gate(initial_witness, &a, &b, result, num_bits, true)
-    }
+/// Solves a [`BlackBoxFunc::XOR`][acir::circuit::black_box_functions::BlackBoxFunc::XOR] opcode and inserts
+/// the result into the supplied witness map
+pub fn xor(
+    initial_witness: &mut BTreeMap<Witness, FieldElement>,
+    gate: &BlackBoxFuncCall,
+) -> Result<OpcodeResolution, OpcodeResolutionError> {
+    let (a, b, result, num_bits) = extract_input_output(gate);
+    solve_logic_gate(initial_witness, &a, &b, result, |left, right| left.xor(right, num_bits))
 }
+
 // TODO: Is there somewhere else that we can put this?
 // TODO: extraction methods are needed for some opcodes like logic and range
 pub(crate) fn extract_input_output(
@@ -69,3 +39,19 @@ pub(crate) fn extract_input_output(
 
     (a.witness, b.witness, *result, num_bits)
 }
+
+/// Derives the rest of the witness based on the initial low level variables
+fn solve_logic_gate(
+    initial_witness: &mut BTreeMap<Witness, FieldElement>,
+    a: &Witness,
+    b: &Witness,
+    result: Witness,
+    logic_op: impl Fn(&FieldElement, &FieldElement) -> FieldElement,
+) -> Result<OpcodeResolution, OpcodeResolutionError> {
+    let w_l_value = witness_to_value(initial_witness, *a)?;
+    let w_r_value = witness_to_value(initial_witness, *b)?;
+    let assignment = logic_op(w_l_value, w_r_value);
+
+    insert_value(&result, assignment, initial_witness)?;
+    Ok(OpcodeResolution::Solved)
+}