remove rng from context and use thread local rng

src/ffi.rs

@@ -10,7 +10,7 @@ use ark_bn254::{Bn254, Fr};
 use ark_circom::{read_zkey, CircomBuilder, CircomConfig, CircomReduction};
 use ark_crypto_primitives::snark::SNARK;
 use ark_groth16::{prepare_verifying_key, Groth16, ProvingKey};
-use ark_std::rand::{rngs::ThreadRng, thread_rng};
+use ark_std::rand::thread_rng;
 use ruint::aliases::U256;
 
 use crate::ffi_types::*;
@@ -50,7 +50,6 @@ struct CircomBn254 {
 #[derive(Debug, Clone)]
 struct CircomCompatCtx {
     circom: *mut CircomBn254,
-    rng: ThreadRng,
     _marker: core::marker::PhantomData<(*mut CircomCompatCtx, core::marker::PhantomPinned)>,
 }
 
@@ -144,7 +143,6 @@ pub unsafe extern "C" fn init_circom_compat(
     ctx_ptr: &mut *mut CircomCompatCtx,
 ) -> i32 {
     let result = catch_unwind(AssertUnwindSafe(|| {
-        let rng = thread_rng(); // TODO: use a shared rng - how?
         let builder = CircomBuilder::new((*(*cfg_ptr).cfg).clone()); // clone the config
         let circom_bn254 = CircomBn254 {
             builder: Box::into_raw(Box::new(builder)),
@@ -153,7 +151,6 @@ pub unsafe extern "C" fn init_circom_compat(
 
         let circom_compat_ctx = CircomCompatCtx {
             circom: Box::into_raw(Box::new(circom_bn254)),
-            rng: rng,
             _marker: core::marker::PhantomData,
         };
 
@@ -242,7 +239,7 @@ pub unsafe extern "C" fn prove_circuit(
     let result = catch_unwind(AssertUnwindSafe(|| {
         let circom = &mut *to_circom(ctx_ptr);
         let proving_key = (*(*cfg_ptr).proving_key).clone();
-        let rng = &mut (*ctx_ptr).rng;
+        let rng = &mut thread_rng();
 
         let circuit = (*circom.builder)
             .clone()