feat: implement bigint in Noir, using bigint opcodes

noir/compiler/noirc_evaluator/src/errors.rs

@@ -44,6 +44,8 @@ pub enum RuntimeError {
     AssertConstantFailed { call_stack: CallStack },
     #[error("Nested slices are not supported")]
     NestedSlice { call_stack: CallStack },
+    #[error("Big Integer modulus do no match")]
+    BigIntModulus { call_stack: CallStack },
 }
 
 // We avoid showing the actual lhs and rhs since most of the time they are just 0
@@ -132,7 +134,8 @@ impl RuntimeError {
             | RuntimeError::AssertConstantFailed { call_stack }
             | RuntimeError::IntegerOutOfBounds { call_stack, .. }
             | RuntimeError::UnsupportedIntegerSize { call_stack, .. }
-            | RuntimeError::NestedSlice { call_stack, .. } => call_stack,
+            | RuntimeError::NestedSlice { call_stack, .. }
+            | RuntimeError::BigIntModulus { call_stack, .. } => call_stack,
         }
     }
 }

noir/compiler/noirc_evaluator/src/ssa/acir_gen/acir_ir.rs

@@ -1,3 +1,4 @@
 pub(crate) mod acir_variable;
+pub(crate) mod big_int;
 pub(crate) mod generated_acir;
 pub(crate) mod sort;

noir/compiler/noirc_evaluator/src/ssa/acir_gen/acir_ir/acir_variable.rs

@@ -1,3 +1,4 @@
+use super::big_int::BigIntContext;
 use super::generated_acir::GeneratedAcir;
 use crate::brillig::brillig_gen::brillig_directive;
 use crate::brillig::brillig_ir::artifact::GeneratedBrillig;
@@ -107,6 +108,9 @@ pub(crate) struct AcirContext {
     /// then the `acir_ir` will be populated to assert this
     /// addition.
     acir_ir: GeneratedAcir,
+
+    /// The BigIntContext, used to generate identifiers for BigIntegers
+    big_int_ctx: BigIntContext,
 }
 
 impl AcirContext {
@@ -1140,10 +1144,10 @@ impl AcirContext {
         &mut self,
         name: BlackBoxFunc,
         mut inputs: Vec<AcirValue>,
-        output_count: usize,
+        mut output_count: usize,
     ) -> Result<Vec<AcirVar>, RuntimeError> {
         // Separate out any arguments that should be constants
-        let constants = match name {
+        let (constant_inputs, constant_outputs) = match name {
             BlackBoxFunc::PedersenCommitment | BlackBoxFunc::PedersenHash => {
                 // The last argument of pedersen is the domain separator, which must be a constant
                 let domain_var = match inputs.pop() {
@@ -1167,23 +1171,116 @@ impl AcirContext {
                     }
                 };
 
-                vec![domain_constant]
+                (vec![domain_constant], Vec::new())
+            }
+            BlackBoxFunc::BigIntAdd
+            | BlackBoxFunc::BigIntNeg
+            | BlackBoxFunc::BigIntMul
+            | BlackBoxFunc::BigIntDiv => {
+                assert_eq!(inputs.len(), 4, "ICE - bigint operation requires 4 inputs");
+                let const_inputs = vecmap(inputs, |i| {
+                    let var = i.into_var()?;
+                    match self.vars[&var].as_constant() {
+                        Some(const_var) => Ok(const_var),
+                        None => Err(RuntimeError::InternalError(InternalError::NotAConstant {
+                            name: "big integer".to_string(),
+                            call_stack: self.get_call_stack(),
+                        })),
+                    }
+                });
+                inputs = Vec::new();
+                output_count = 0;
+                let mut field_inputs = Vec::new();
+                for i in const_inputs {
+                    field_inputs.push(i?);
+                }
+                if field_inputs[1] != field_inputs[3] {
+                    return Err(RuntimeError::BigIntModulus { call_stack: self.get_call_stack() });
+                }
+
+                let result_id = self.big_int_ctx.new_big_int(field_inputs[1]);
+                (
+                    vec![field_inputs[0], field_inputs[2]],
+                    vec![result_id.as_field(), result_id.modulus_id()],
+                )
+            }
+            BlackBoxFunc::BigIntToLeBytes => {
+                let const_inputs = vecmap(inputs, |i| {
+                    let var = i.into_var()?;
+                    match self.vars[&var].as_constant() {
+                        Some(const_var) => Ok(const_var),
+                        None => Err(RuntimeError::InternalError(InternalError::NotAConstant {
+                            name: "big integer".to_string(),
+                            call_stack: self.get_call_stack(),
+                        })),
+                    }
+                });
+                inputs = Vec::new();
+                let mut field_inputs = Vec::new();
+                for i in const_inputs {
+                    field_inputs.push(i?);
+                }
+                let modulus = self.big_int_ctx.modulus(field_inputs[0]);
+                let bytes_nb = ((modulus - BigUint::from(1_u32)).bits() - 1) / 8 + 1;
+                output_count = bytes_nb as usize;
+                (field_inputs, vec![FieldElement::from(bytes_nb as u128)])
+            }
+            BlackBoxFunc::BigIntFromLeBytes => {
+                let invalid_input = "ICE - bigint operation requires 2 inputs";
+                assert_eq!(inputs.len(), 2, "{invalid_input}");
+                let mut modulus = Vec::new();
+                match inputs.pop().expect(invalid_input) {
+                    AcirValue::Array(values) => {
+                        for value in values {
+                            modulus.push(self.vars[&value.into_var()?].as_constant().ok_or(
+                                RuntimeError::InternalError(InternalError::NotAConstant {
+                                    name: "big integer".to_string(),
+                                    call_stack: self.get_call_stack(),
+                                }),
+                            )?);
+                        }
+                    }
+                    _ => {
+                        return Err(RuntimeError::InternalError(InternalError::MissingArg {
+                            name: "big_int_from_le_bytes".to_owned(),
+                            arg: "modulus".to_owned(),
+                            call_stack: self.get_call_stack(),
+                        }));
+                    }
+                }
+                let big_modulus = BigUint::from_bytes_le(&vecmap(&modulus, |b| b.to_u128() as u8));
+                output_count = 0;
+
+                let modulus_id = self.big_int_ctx.get_or_insert_modulus(big_modulus);
+                let result_id =
+                    self.big_int_ctx.new_big_int(FieldElement::from(modulus_id as u128));
+                (modulus, vec![result_id.as_field(), result_id.modulus_id()])
             }
-            _ => vec![],
+            _ => (vec![], vec![]),
         };
 
         // Convert `AcirVar` to `FunctionInput`
         let inputs = self.prepare_inputs_for_black_box_func_call(inputs)?;
 
         // Call Black box with `FunctionInput`
-        let outputs = self.acir_ir.call_black_box(name, &inputs, constants, output_count)?;
+        let mut results = vecmap(&constant_outputs, |c| self.add_constant(*c));
+        let outputs = self.acir_ir.call_black_box(
+            name,
+            &inputs,
+            constant_inputs,
+            constant_outputs,
+            output_count,
+        )?;
 
         // Convert `Witness` values which are now constrained to be the output of the
         // black box function call into `AcirVar`s.
         //
         // We do not apply range information on the output of the black box function.
         // See issue #1439
-        Ok(vecmap(&outputs, |witness_index| self.add_data(AcirVarData::Witness(*witness_index))))
+        results.extend(vecmap(&outputs, |witness_index| {
+            self.add_data(AcirVarData::Witness(*witness_index))
+        }));
+        Ok(results)
     }
 
     /// Black box function calls expect their inputs to be in a specific data structure (FunctionInput).

noir/compiler/noirc_evaluator/src/ssa/acir_gen/acir_ir/big_int.rs

@@ -0,0 +1,54 @@
+use acvm::FieldElement;
+use num_bigint::BigUint;
+
+/// Represents a bigint value in the form (id, modulus) where
+///     id is the identifier of the big integer number, and
+///     modulus is the identifier of the big integer size
+#[derive(Default, Clone, Copy, Debug)]
+pub(crate) struct BigIntId(pub(crate) u32, pub(crate) u32); //bigint id, modulus id
+
+impl BigIntId {
+    pub(crate) fn as_field(&self) -> FieldElement {
+        FieldElement::from(self.0 as u128)
+    }
+
+    pub(crate) fn modulus_id(&self) -> FieldElement {
+        FieldElement::from(self.1 as u128)
+    }
+}
+
+/// BigIntContext is used to generate identifiers for big integers and their modulus
+#[derive(Default, Debug)]
+pub(crate) struct BigIntContext {
+    modulus: Vec<BigUint>,
+    big_integers: Vec<BigIntId>,
+}
+
+impl BigIntContext {
+    /// Creates a new BigIntId for the given modulus and returns it.
+    pub(crate) fn new_big_int(&mut self, modulus: FieldElement) -> BigIntId {
+        let id = self.big_integers.len() as u32;
+        let result = BigIntId(id, modulus.to_u128() as u32);
+        self.big_integers.push(result);
+        result
+    }
+
+    /// Returns the modulus corresponding to the given modulus index
+    pub(crate) fn modulus(&self, idx: FieldElement) -> BigUint {
+        self.modulus[idx.to_u128() as usize].clone()
+    }
+
+    /// Returns the BigIntId corresponding to the given identifier
+    pub(crate) fn get(&self, id: FieldElement) -> BigIntId {
+        self.big_integers[id.to_u128() as usize]
+    }
+
+    /// Adds a modulus to the context (if it is not already present)
+    pub(crate) fn get_or_insert_modulus(&mut self, modulus: BigUint) -> u32 {
+        if let Some(pos) = self.modulus.iter().position(|x| x == &modulus) {
+            return pos as u32;
+        }
+        self.modulus.push(modulus);
+        (self.modulus.len() - 1) as u32
+    }
+}

noir/compiler/noirc_evaluator/src/ssa/acir_gen/acir_ir/generated_acir.rs

@@ -138,7 +138,8 @@ impl GeneratedAcir {
         &mut self,
         func_name: BlackBoxFunc,
         inputs: &[Vec<FunctionInput>],
-        constants: Vec<FieldElement>,
+        constant_inputs: Vec<FieldElement>,
+        constant_outputs: Vec<FieldElement>,
         output_count: usize,
     ) -> Result<Vec<Witness>, InternalError> {
         let input_count = inputs.iter().fold(0usize, |sum, val| sum + val.len());
@@ -176,12 +177,12 @@ impl GeneratedAcir {
             BlackBoxFunc::PedersenCommitment => BlackBoxFuncCall::PedersenCommitment {
                 inputs: inputs[0].clone(),
                 outputs: (outputs[0], outputs[1]),
-                domain_separator: constants[0].to_u128() as u32,
+                domain_separator: constant_inputs[0].to_u128() as u32,
             },
             BlackBoxFunc::PedersenHash => BlackBoxFuncCall::PedersenHash {
                 inputs: inputs[0].clone(),
                 output: outputs[0],
-                domain_separator: constants[0].to_u128() as u32,
+                domain_separator: constant_inputs[0].to_u128() as u32,
             },
             BlackBoxFunc::EcdsaSecp256k1 => {
                 BlackBoxFuncCall::EcdsaSecp256k1 {
@@ -252,33 +253,34 @@ impl GeneratedAcir {
                 key_hash: inputs[3][0],
             },
             BlackBoxFunc::BigIntAdd => BlackBoxFuncCall::BigIntAdd {
-                lhs: constants[0].to_u128() as u32,
-                rhs: constants[1].to_u128() as u32,
-                output: constants[2].to_u128() as u32,
+                lhs: constant_inputs[0].to_u128() as u32,
+                rhs: constant_inputs[1].to_u128() as u32,
+                output: constant_outputs[0].to_u128() as u32,
             },
             BlackBoxFunc::BigIntNeg => BlackBoxFuncCall::BigIntNeg {
-                lhs: constants[0].to_u128() as u32,
-                rhs: constants[1].to_u128() as u32,
-                output: constants[2].to_u128() as u32,
+                lhs: constant_inputs[0].to_u128() as u32,
+                rhs: constant_inputs[1].to_u128() as u32,
+                output: constant_outputs[0].to_u128() as u32,
             },
             BlackBoxFunc::BigIntMul => BlackBoxFuncCall::BigIntMul {
-                lhs: constants[0].to_u128() as u32,
-                rhs: constants[1].to_u128() as u32,
-                output: constants[2].to_u128() as u32,
+                lhs: constant_inputs[0].to_u128() as u32,
+                rhs: constant_inputs[1].to_u128() as u32,
+                output: constant_outputs[0].to_u128() as u32,
             },
             BlackBoxFunc::BigIntDiv => BlackBoxFuncCall::BigIntDiv {
-                lhs: constants[0].to_u128() as u32,
-                rhs: constants[1].to_u128() as u32,
-                output: constants[2].to_u128() as u32,
+                lhs: constant_inputs[0].to_u128() as u32,
+                rhs: constant_inputs[1].to_u128() as u32,
+                output: constant_outputs[0].to_u128() as u32,
             },
             BlackBoxFunc::BigIntFromLeBytes => BlackBoxFuncCall::BigIntFromLeBytes {
                 inputs: inputs[0].clone(),
-                modulus: vecmap(constants, |c| c.to_u128() as u8),
-                output: todo!(),
+                modulus: vecmap(constant_inputs, |c| c.to_u128() as u8),
+                output: constant_outputs[0].to_u128() as u32,
+            },
+            BlackBoxFunc::BigIntToLeBytes => BlackBoxFuncCall::BigIntToLeBytes {
+                input: constant_inputs[0].to_u128() as u32,
+                outputs,
             },
-            BlackBoxFunc::BigIntToLeBytes => {
-                BlackBoxFuncCall::BigIntToLeBytes { input: constants[0].to_u128() as u32, outputs }
-            }
         };
 
         self.push_opcode(AcirOpcode::BlackBoxFuncCall(black_box_func_call));
@@ -636,16 +638,15 @@ fn black_box_func_expected_input_size(name: BlackBoxFunc) -> Option<usize> {
         // Doubling over the embedded curve: input is (x,y) coordinate of the point.
         BlackBoxFunc::EmbeddedCurveDouble => Some(2),
 
-        // Big integer operations take in 2 inputs
+        // Big integer operations take in 0 inputs. They use constants for their inputs.
         BlackBoxFunc::BigIntAdd
         | BlackBoxFunc::BigIntNeg
         | BlackBoxFunc::BigIntMul
-        | BlackBoxFunc::BigIntDiv => Some(2),
+        | BlackBoxFunc::BigIntDiv
+        | BlackBoxFunc::BigIntToLeBytes => Some(0),
 
         // FromLeBytes takes a variable array of bytes as input
         BlackBoxFunc::BigIntFromLeBytes => None,
-        // ToLeBytes takes a single big integer as input
-        BlackBoxFunc::BigIntToLeBytes => Some(1),
     }
 }
 
@@ -691,7 +692,7 @@ fn black_box_expected_output_size(name: BlackBoxFunc) -> Option<usize> {
         | BlackBoxFunc::BigIntNeg
         | BlackBoxFunc::BigIntMul
         | BlackBoxFunc::BigIntDiv
-        | BlackBoxFunc::BigIntFromLeBytes => Some(1),
+        | BlackBoxFunc::BigIntFromLeBytes => Some(0),
 
         // ToLeBytes returns a variable array of bytes
         BlackBoxFunc::BigIntToLeBytes => None,
@@ -752,5 +753,5 @@ fn intrinsics_check_outputs(name: BlackBoxFunc, output_count: usize) {
         None => return,
     };
 
-    assert_eq!(expected_num_outputs,output_count,"Tried to call black box function {name} with {output_count} inputs, but this function's definition requires {expected_num_outputs} inputs");
+    assert_eq!(expected_num_outputs,output_count,"Tried to call black box function {name} with {output_count} outputs, but this function's definition requires {expected_num_outputs} outputs");
 }

noir/compiler/noirc_evaluator/src/ssa/acir_gen/mod.rs

@@ -1541,7 +1541,7 @@ impl Context {
 
                 let vars = self.acir_context.black_box_function(black_box, inputs, output_count)?;
 
-                Ok(Self::convert_vars_to_values(vars, dfg, result_ids))
+                Ok(self.convert_vars_to_values(vars, dfg, result_ids))
             }
             Intrinsic::ApplyRangeConstraint => {
                 unreachable!("ICE: `Intrinsic::ApplyRangeConstraint` calls should be transformed into an `Instruction::RangeCheck`");
@@ -1588,7 +1588,7 @@ impl Context {
                     .sort(input_vars, bit_size, self.current_side_effects_enabled_var)
                     .expect("Could not sort");
 
-                Ok(Self::convert_vars_to_values(out_vars, dfg, result_ids))
+                Ok(self.convert_vars_to_values(out_vars, dfg, result_ids))
             }
             Intrinsic::ArrayLen => {
                 let len = match self.convert_value(arguments[0], dfg) {
@@ -2101,16 +2101,35 @@ impl Context {
     /// Convert a Vec<AcirVar> into a Vec<AcirValue> using the given result ids.
     /// If the type of a result id is an array, several acir vars are collected into
     /// a single AcirValue::Array of the same length.
+    /// If the type of a result id is a slice, the slice length must precede it and we can
+    /// convert to an AcirValue::Array when the length is known (constant).
     fn convert_vars_to_values(
+        &self,
         vars: Vec<AcirVar>,
         dfg: &DataFlowGraph,
         result_ids: &[ValueId],
     ) -> Vec<AcirValue> {
         let mut vars = vars.into_iter();
-        vecmap(result_ids, |result| {
+        let mut values: Vec<AcirValue> = Vec::new();
+        for result in result_ids {
             let result_type = dfg.type_of_value(*result);
-            Self::convert_var_type_to_values(&result_type, &mut vars)
-        })
+            if let Type::Slice(elements_type) = result_type {
+                let error = "ICE - cannot get slice length when converting slice to AcirValue";
+                let len = values.last().expect(error).borrow_var().expect(error);
+                let len = self.acir_context.constant(len).to_u128();
+                let mut element_values = im::Vector::new();
+                for _ in 0..len {
+                    for element_type in elements_type.iter() {
+                        let element = Self::convert_var_type_to_values(element_type, &mut vars);
+                        element_values.push_back(element);
+                    }
+                }
+                values.push(AcirValue::Array(element_values));
+            } else {
+                values.push(Self::convert_var_type_to_values(&result_type, &mut vars));
+            }
+        }
+        values
     }
 
     /// Recursive helper for convert_vars_to_values.