Parallel proof of work + Update Rayon (#645)

* Parallel proof of work

* Fmt

* Fix clippy

provers/cairo/Cargo.toml

@@ -34,7 +34,7 @@ serde_cbor = { version = "0.11.1" }
 # For cli
 clap = { version = "4.4.6", features = ["derive"], optional = true }
 # Parallelization crates
-rayon = { version = "1.7.0", optional = true }
+rayon = { version = "1.8.0", optional = true }
 
 # wasm
 wasm-bindgen = { version = "0.2", optional = true }

provers/stark/Cargo.toml

@@ -23,7 +23,7 @@ num-integer = "0.1.45"
 itertools = "0.11.0"
 
 # Parallelization crates
-rayon = { version = "1.7.0", optional = true }
+rayon = { version = "1.8.0", optional = true }
 
 # wasm
 wasm-bindgen = { version = "0.2", optional = true }

provers/stark/src/grinding.rs

@@ -1,3 +1,5 @@
+#[cfg(feature = "parallel")]
+use rayon::prelude::{IntoParallelIterator, ParallelIterator};
 use sha3::{Digest, Keccak256};
 
 const PREFIX: [u8; 8] = [0x01, 0x23, 0x45, 0x67, 0x89, 0xab, 0xcd, 0xed];
@@ -38,8 +40,16 @@ pub fn is_valid_nonce(seed: &[u8; 32], nonce: u64, grinding_factor: u8) -> bool
 pub fn generate_nonce(seed: &[u8; 32], grinding_factor: u8) -> Option<u64> {
     let inner_hash = get_inner_hash(seed, grinding_factor);
     let limit = 1 << (64 - grinding_factor);
-    (0..u64::MAX)
-        .find(|&candidate_nonce| is_valid_nonce_for_inner_hash(&inner_hash, candidate_nonce, limit))
+
+    #[cfg(not(feature = "parallel"))]
+    return (0..u64::MAX).find(|&candidate_nonce| {
+        is_valid_nonce_for_inner_hash(&inner_hash, candidate_nonce, limit)
+    });
+
+    #[cfg(feature = "parallel")]
+    return (0..u64::MAX).into_par_iter().find_any(|&candidate_nonce| {
+        is_valid_nonce_for_inner_hash(&inner_hash, candidate_nonce, limit)
+    });
 }
 
 /// Checks if the leftmost 8 bytes of `Hash(inner_hash || candidate_nonce)` are less than `limit`