feat(stdlib): grumpkin scalar multiplication API (#2586)

Co-authored-by: kevaundray <[email protected]>

noir_stdlib/src/grumpkin_scalar.nr

@@ -0,0 +1,21 @@
+struct GrumpkinScalar {
+    low: Field,
+    high: Field,
+}
+
+impl GrumpkinScalar {
+    fn new(low: Field, high: Field) -> Self {
+        // TODO: check that the low and high value fit within the grumpkin modulus
+        GrumpkinScalar { low, high }
+    }
+}
+
+global GRUMPKIN_SCALAR_SERIALISED_LEN: Field = 2;
+
+fn deserialise_grumpkin_scalar(fields: [Field; GRUMPKIN_SCALAR_SERIALISED_LEN]) -> GrumpkinScalar {
+    GrumpkinScalar { low: fields[0], high: fields[1] }
+}
+
+fn serialise_grumpkin_scalar(scalar: GrumpkinScalar) -> [Field; GRUMPKIN_SCALAR_SERIALISED_LEN] {
+    [scalar.low, scalar.high]
+}

noir_stdlib/src/grumpkin_scalar_mul.nr

@@ -0,0 +1,7 @@
+use crate::grumpkin_scalar::GrumpkinScalar;
+use crate::scalar_mul::fixed_base_embedded_curve;
+
+fn grumpkin_fixed_base(scalar: GrumpkinScalar) -> [Field; 2] {
+    // TODO: this should use both the low and high limbs to do the scalar multiplication
+    fixed_base_embedded_curve(scalar.low)
+}

noir_stdlib/src/lib.nr

@@ -6,6 +6,8 @@ mod schnorr;
 mod ecdsa_secp256k1;
 mod ecdsa_secp256r1;
 mod eddsa;
+mod grumpkin_scalar;
+mod grumpkin_scalar_mul;
 mod scalar_mul;
 mod sha256;
 mod sha512;