feat(std_lib)!: modulus bits and modulus bytes methods

crates/nargo/tests/test_data/7_function/src/main.nr

@@ -33,7 +33,7 @@ fn test2(z: Field, t: u32 ) {
 
 fn pow(base: Field, exponent: Field) -> Field {
     let mut r = 1 as Field;
-    let b = std::to_bits(exponent, 32 as u32);
+    let b = std::field::to_le_bits(exponent, 32 as u32);
     for i in 1..33 {
         r = r*r;
         r = (b[32-i] as Field) * (r * base) + (1 - b[32-i] as Field) * r;

crates/nargo/tests/test_data/9_conditional/src/main.nr

@@ -59,12 +59,12 @@ fn main(a: u32, mut c: [u32; 4], x: [u8; 5], result: pub [u8; 32]){
         }
     }
 
-    //Regression for to_bits() constant evaluation 
+    //Regression for to_le_bits() constant evaluation 
     // binary array representation of u8 1
     let as_bits_hardcode_1 = [1, 0];
     let mut c1 = 0;
     for i in 0..2 {
-        let mut as_bits = std::to_bits(arr[i] as Field, 2);
+        let mut as_bits = std::field::to_le_bits(arr[i] as Field, 2);
         c1 = c1 + as_bits[0] as Field;
 
         if i == 0 {

crates/nargo/tests/test_data/modulus/Nargo.toml

@@ -0,0 +1,5 @@
+[package]
+authors = [""]
+compiler_version = "0.1"
+
+[dependencies]

crates/nargo/tests/test_data/modulus/Prover.toml

@@ -0,0 +1,3 @@
+bn254_modulus_be_bytes = [48, 100, 78, 114, 225, 49, 160, 41, 184, 80, 69, 182, 129, 129, 88, 93, 40, 51, 232, 72, 121, 185, 112, 145, 67, 225, 245, 147, 240, 0, 0, 1]
+bn254_modulus_be_bits = [1, 1, 0, 0, 0, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 1, 1, 0, 0, 1, 1, 1, 0, 0, 1, 0, 1, 1, 1, 0, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 0, 1, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 1, 1, 0, 1, 1, 1, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 1, 1, 0, 0, 0, 0, 1, 0, 1, 1, 1, 0, 1, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 1, 0, 0, 1, 1, 1, 1, 1, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 1, 1, 0, 1, 1, 1, 0, 0, 1, 0, 1, 1, 1, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 1, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 1, 0, 0, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1]
+return = ""

crates/nargo/tests/test_data/modulus/src/main.nr

@@ -0,0 +1,27 @@
+use dep::std;
+
+fn main(bn254_modulus_be_bytes : [u8; 32], bn254_modulus_be_bits : [u1; 254]) -> pub Field {
+    let modulus_size = std::field::modulus_num_bits();
+    // NOTE: The constraints used in this circuit will only work when testing nargo with the plonk bn254 backend
+    constrain modulus_size == 254;
+
+    let modulus_be_byte_array = std::field::modulus_be_bytes();
+    for i in 0..32 {
+        constrain modulus_be_byte_array[i] == bn254_modulus_be_bytes[i];
+    }
+    let modulus_le_byte_array = std::field::modulus_le_bytes();
+    for i in 0..32 {
+        constrain modulus_le_byte_array[i] == bn254_modulus_be_bytes[31-i];
+    }
+
+    let modulus_be_bits = std::field::modulus_be_bits();
+    for i in 0..254 {
+        constrain modulus_be_bits[i] == bn254_modulus_be_bits[i];
+    }
+    let modulus_le_bits = std::field::modulus_le_bits();
+    for i in 0..254 {
+        constrain modulus_le_bits[i] == bn254_modulus_be_bits[253-i];
+    }
+
+    modulus_size
+}

crates/nargo/tests/test_data/to_le_bytes/Prover.toml

@@ -1,2 +1,2 @@
 x = "2040124"
-return = [0x3c, 0x21, 0x1f, 0x00]
+return = [0x3c, 0x21, 0x1f, 0x00]

crates/nargo/tests/test_data/to_le_bytes/src/main.nr

@@ -2,7 +2,7 @@ use dep::std;
 
 fn main(x : Field) -> pub [u8; 4] {
     // The result of this byte array will be little-endian
-    let byte_array = std::to_le_bytes(x, 31);
+    let byte_array = std::field::to_le_bytes(x, 31);
     let mut first_four_bytes = [0; 4];
     for i in 0..4 {
         first_four_bytes[i] = byte_array[i];

crates/noirc_evaluator/src/ssa/builtin.rs

@@ -20,7 +20,7 @@ impl std::fmt::Display for Opcode {
 impl Opcode {
     pub fn lookup(op_name: &str) -> Option<Opcode> {
         match op_name {
-            "to_bits" => Some(Opcode::ToBits),
+            "to_le_bits" => Some(Opcode::ToBits),
             "to_radix" => Some(Opcode::ToRadix),
             _ => BlackBoxFunc::lookup(op_name).map(Opcode::LowLevel),
         }
@@ -29,7 +29,7 @@ impl Opcode {
     pub fn name(&self) -> &str {
         match self {
             Opcode::LowLevel(op) => op.name(),
-            Opcode::ToBits => "to_bits",
+            Opcode::ToBits => "to_le_bits",
             Opcode::ToRadix => "to_radix",
         }
     }

crates/noirc_evaluator/src/ssa/optim.rs

@@ -362,7 +362,7 @@ fn cse_block_with_anchor(
                 result?;
             }
 
-            //cannot simplify to_bits() in the previous call because it get replaced with multiple instructions
+            //cannot simplify to_le_bits() in the previous call because it get replaced with multiple instructions
             if let Operation::Intrinsic(opcode, args) = &update2.operation {
                 let args = args.iter().map(|arg| {
                     NodeEval::from_id(ctx, *arg).into_const_value().map(|f| f.to_u128())

crates/noirc_frontend/src/monomorphisation/mod.rs

@@ -1,3 +1,4 @@
+use acvm::FieldElement;
 use iter_extended::{btree_map, vecmap};
 use noirc_abi::Abi;
 use std::collections::{BTreeMap, HashMap, VecDeque};
@@ -574,7 +575,7 @@ impl Monomorphiser {
         }))
     }
 
-    /// Try to evaluate certain builtin functions (currently only 'arraylen')
+    /// Try to evaluate certain builtin functions (currently only 'arraylen' and field modulus methods)
     /// at their callsite.
     /// NOTE: Evaluating at the callsite means we cannot track aliased functions.
     ///       E.g. `let f = std::array::len; f(arr)` will fail to evaluate.
@@ -595,12 +596,52 @@ impl Monomorphiser {
                         ast::Type::Field,
                     )))
                 }
+                Definition::Builtin(opcode) if opcode == "modulus_num_bits" => {
+                    Some(ast::Expression::Literal(ast::Literal::Integer(
+                        (FieldElement::max_num_bits() as u128).into(),
+                        ast::Type::Field,
+                    )))
+                }
+                Definition::Builtin(opcode) if opcode == "modulus_le_bits" => {
+                    let modulus = FieldElement::modulus();
+                    let bits = modulus.to_radix_le(2);
+                    Some(self.modulus_array_literal(bits, 1))
+                }
+                Definition::Builtin(opcode) if opcode == "modulus_be_bits" => {
+                    let modulus = FieldElement::modulus();
+                    let bits = modulus.to_radix_be(2);
+                    Some(self.modulus_array_literal(bits, 1))
+                }
+                Definition::Builtin(opcode) if opcode == "modulus_be_bytes" => {
+                    let modulus = FieldElement::modulus();
+                    let bytes = modulus.to_bytes_be();
+                    Some(self.modulus_array_literal(bytes, 8))
+                }
+                Definition::Builtin(opcode) if opcode == "modulus_le_bytes" => {
+                    let modulus = FieldElement::modulus();
+                    let bytes = modulus.to_bytes_le();
+                    Some(self.modulus_array_literal(bytes, 8))
+                }
                 _ => None,
             },
             _ => None,
         }
     }
 
+    fn modulus_array_literal(&self, bytes: Vec<u8>, arr_elem_bits: u32) -> ast::Expression {
+        let bytes_as_expr = vecmap(bytes, |byte| {
+            ast::Expression::Literal(ast::Literal::Integer(
+                (byte as u128).into(),
+                ast::Type::Integer(crate::Signedness::Unsigned, arr_elem_bits),
+            ))
+        });
+        let arr_literal = ast::ArrayLiteral {
+            contents: bytes_as_expr,
+            element_type: ast::Type::Integer(crate::Signedness::Unsigned, arr_elem_bits),
+        };
+        ast::Expression::Literal(ast::Literal::Array(arr_literal))
+    }
+
     fn queue_function(
         &mut self,
         id: node_interner::FuncId,

noir_stdlib/src/field.nr

@@ -0,0 +1,26 @@
+#[builtin(to_le_bits)]
+fn to_le_bits(_x : Field, _bit_size: u32) -> [u1] {}
+
+fn to_le_bytes(x : Field, byte_size: u32) -> [u8] {
+    to_radix(x, 256, byte_size)
+}
+
+#[builtin(to_radix)]
+//decompose _x into a _result_len vector over the _radix basis
+//_radix must be less than 256
+fn to_radix(_x : Field, _radix: u32, _result_len: u32) -> [u8] {}
+
+#[builtin(modulus_num_bits)]
+fn modulus_num_bits() -> comptime Field {}
+
+#[builtin(modulus_be_bits)]
+fn modulus_be_bits() -> [u1] {}
+
+#[builtin(modulus_le_bits)]
+fn modulus_le_bits() -> [u1] {}
+
+#[builtin(modulus_be_bytes)]
+fn modulus_be_bytes() -> [u8] {}
+
+#[builtin(modulus_le_bytes)]
+fn modulus_le_bytes() -> [u8] {}

noir_stdlib/src/lib.nr

@@ -6,29 +6,15 @@ mod ecdsa_secp256k1;
 mod scalar_mul;
 mod sha256;
 mod sha512;
-
-
- #[builtin(to_bits)]
-fn to_bits(_x : Field, _bit_size: u32) -> [u1] {}
-
-fn to_le_bytes(x : Field, byte_size: u32) -> [u8] {
-    to_radix(x, 256, byte_size)
-}
-
-#[builtin(to_radix)]
-//decompose _x into a _result_len vector over the _radix basis
-//_radix must be less than 256
-fn to_radix(_x : Field, _radix: u32, _result_len: u32) -> [u8] {}
-
-
+mod field;
 
 // Returns base^exponent. 
 // ^ means to the power of and not xor
 // Caution: we assume the exponent fits into 32 bits
 // using a bigger bit size impacts negatively the performance and should be done only if the exponent does not fit in 32 bits
 fn pow_32(base: Field, exponent: Field) -> Field {
     let mut r = 1 as Field;
-    let b = crate::to_bits(exponent, 32);
+    let b = field::to_le_bits(exponent, 32);
 
     for i in 1..33 {
         r = r*r;

noir_stdlib/src/merkle.nr

@@ -17,7 +17,7 @@ fn check_membership_in_noir(root : Field, leaf : Field, index : Field, hash_path
 // Returns the root of the tree from the provided leaf and its hashpath, using pedersen hash
 fn compute_root_from_leaf(leaf : Field, index : Field, hash_path: [Field]) -> Field {
     let n = crate::array::len(hash_path);
-    let index_bits = crate::to_bits(index, n as u32);
+    let index_bits = crate::field::to_le_bits(index, n as u32);
     let mut current = leaf;
     for i in 0..n {
         let path_bit = index_bits[i] as bool;