feat: cache default generators to avoid recalculating

acvm-repo/bn254_blackbox_solver/src/generator/generators.rs

@@ -1,5 +1,7 @@
 // Taken from https://github.com/laudiacay/barustenberg/blob/df6bc6f095fe7f288bf6a12e7317fd8eb33d68ae/barustenberg/src/ecc/groups/affine_element.rshttps://github.com/laudiacay/barustenberg/blob/df6bc6f095fe7f288bf6a12e7317fd8eb33d68ae/barustenberg/src/ecc/groups/group.rs
 
+use std::sync::OnceLock;
+
 use ark_ec::short_weierstrass::Affine;
 
 use acvm_blackbox_solver::blake3;
@@ -8,6 +10,17 @@ use grumpkin::GrumpkinParameters;
 use super::hash_to_curve::hash_to_curve;
 
 pub(crate) const DEFAULT_DOMAIN_SEPARATOR: &[u8] = "DEFAULT_DOMAIN_SEPARATOR".as_bytes();
+const NUM_DEFAULT_GENERATORS: usize = 8;
+
+fn default_generators() -> &'static [Affine<GrumpkinParameters>; NUM_DEFAULT_GENERATORS] {
+    static INSTANCE: OnceLock<[Affine<GrumpkinParameters>; NUM_DEFAULT_GENERATORS]> =
+        OnceLock::new();
+    INSTANCE.get_or_init(|| {
+        _derive_generators(DEFAULT_DOMAIN_SEPARATOR, NUM_DEFAULT_GENERATORS as u32, 0)
+            .try_into()
+            .expect("Should generate `NUM_DEFAULT_GENERATORS`")
+    })
+}
 
 /// Derives generator points via [hash-to-curve][hash_to_curve].
 ///
@@ -27,6 +40,21 @@ pub(crate) fn derive_generators(
     domain_separator_bytes: &[u8],
     num_generators: u32,
     starting_index: u32,
+) -> Vec<Affine<GrumpkinParameters>> {
+    // We cache a small number of the default generators so we can reuse them without needing to repeatedly recalculate them.
+    if domain_separator_bytes == DEFAULT_DOMAIN_SEPARATOR && starting_index + num_generators <= NUM_DEFAULT_GENERATORS as u32 {
+        let start_index = starting_index as usize;
+        let end_index = (starting_index + num_generators) as usize;
+        default_generators()[start_index..end_index].to_vec()
+    } else {
+        _derive_generators(domain_separator_bytes, num_generators, starting_index)
+    }
+}
+
+fn _derive_generators(
+    domain_separator_bytes: &[u8],
+    num_generators: u32,
+    starting_index: u32,
 ) -> Vec<Affine<GrumpkinParameters>> {
     let mut generator_preimage = [0u8; 64];
     let domain_hash = blake3(domain_separator_bytes).expect("hash should succeed");

acvm-repo/bn254_blackbox_solver/src/pedersen/hash.rs

@@ -1,5 +1,7 @@
 // Taken from: https://github.com/laudiacay/barustenberg/blob/df6bc6f095fe7f288bf6a12e7317fd8eb33d68ae/barustenberg/src/crypto/pedersen/pederson_hash.rs
 
+use std::sync::OnceLock;
+
 use ark_ec::{short_weierstrass::Affine, CurveConfig, CurveGroup};
 use grumpkin::GrumpkinParameters;
 
@@ -23,14 +25,14 @@ pub(crate) fn hash_with_index(
 ) -> <GrumpkinParameters as CurveConfig>::BaseField {
     let length_as_scalar: <GrumpkinParameters as CurveConfig>::ScalarField =
         (inputs.len() as u64).into();
-    let length_prefix = length_generator(0) * length_as_scalar;
+    let length_prefix = *length_generator() * length_as_scalar;
     let result = length_prefix + commit_native_with_index(inputs, starting_index);
     result.into_affine().x
 }
 
-//Note: this can be abstracted to a lazy_static!()
-fn length_generator(starting_index: u32) -> Affine<GrumpkinParameters> {
-    derive_generators("pedersen_hash_length".as_bytes(), 1, starting_index)[0]
+fn length_generator() -> &'static Affine<GrumpkinParameters> {
+    static INSTANCE: OnceLock<Affine<GrumpkinParameters>> = OnceLock::new();
+    INSTANCE.get_or_init(|| derive_generators("pedersen_hash_length".as_bytes(), 1, 0)[0])
 }
 
 #[cfg(test)]