From a567c8af7a42f8b037eaa44a50d849229bb0f9a9 Mon Sep 17 00:00:00 2001
From: zenground0 <ZenGround0@users.noreply.github.com>
Date: Mon, 26 Aug 2024 11:53:55 -0600
Subject: [PATCH] Reintroduce randomness precompile

---
 actors/evm/src/interpreter/precompiles/fvm.rs | 28 +++++++++++++++++++
 actors/evm/src/interpreter/precompiles/mod.rs |  5 ++--
 runtime/src/runtime/randomness.rs             |  1 +
 3 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/actors/evm/src/interpreter/precompiles/fvm.rs b/actors/evm/src/interpreter/precompiles/fvm.rs
index dd9c52723..121ed40f8 100644
--- a/actors/evm/src/interpreter/precompiles/fvm.rs
+++ b/actors/evm/src/interpreter/precompiles/fvm.rs
@@ -220,3 +220,31 @@ pub(super) fn call_actor_shared<RT: Runtime>(
 
     Ok(output)
 }
+
+/// Params:
+///
+/// | Param            | Value                     |
+/// |------------------|---------------------------|
+/// | randomness_epoch | U256 - low i64             |
+/// | entropy_length   | U256 - low u32             |
+/// | entropy          | input\[32..] (right padded)|
+///
+/// any bytes in between values are ignored
+///
+/// Returns empty array if invalid randomness type
+/// Errors if unable to fetch randomness
+pub(super) fn get_randomness<RT: Runtime>(
+    system: &mut System<RT>,
+    input: &[u8],
+    _: PrecompileContext,
+) -> PrecompileResult {
+
+    let mut input_params = ValueReader::new(input);
+
+    let randomness_epoch = input_params.read_value()?;
+    let entropy_length: u32 = input_params.read_value()?;
+    let entropy = input_params.read_padded(entropy_length.try_into().unwrap_or(0));
+
+    let randomness = system.rt.get_randomness_from_beacon(fil_actors_runtime::runtime::DomainSeparationTag::EvmRandPrecompile, randomness_epoch, &entropy);
+    randomness.map(|r| r.to_vec()).map_err(|_| PrecompileError::InvalidInput)
+}
\ No newline at end of file
diff --git a/actors/evm/src/interpreter/precompiles/mod.rs b/actors/evm/src/interpreter/precompiles/mod.rs
index 5faf7f68d..ddc95d603 100644
--- a/actors/evm/src/interpreter/precompiles/mod.rs
+++ b/actors/evm/src/interpreter/precompiles/mod.rs
@@ -13,7 +13,7 @@ mod evm;
 mod fvm;
 
 use evm::{blake2f, ec_add, ec_mul, ec_pairing, ec_recover, identity, modexp, ripemd160, sha256};
-use fvm::{call_actor, call_actor_id, lookup_delegated_address, resolve_address};
+use fvm::{call_actor, call_actor_id, lookup_delegated_address, resolve_address, get_randomness};
 
 type PrecompileFn<RT> = fn(&mut System<RT>, &[u8], PrecompileContext) -> PrecompileResult;
 pub type PrecompileResult = Result<Vec<u8>, PrecompileError>;
@@ -41,12 +41,13 @@ pub struct Precompiles<RT>(PhantomData<RT>);
 
 impl<RT: Runtime> Precompiles<RT> {
     /// FEVM specific precompiles (0xfe prefix)
-    const NATIVE_PRECOMPILES: PrecompileTable<RT, 5> = PrecompileTable([
+    const NATIVE_PRECOMPILES: PrecompileTable<RT, 6> = PrecompileTable([
         Some(resolve_address::<RT>),          // 0xfe00..01
         Some(lookup_delegated_address::<RT>), // 0xfe00..02
         Some(call_actor::<RT>),               // 0xfe00..03
         None,                                 // 0xfe00..04 DISABLED
         Some(call_actor_id::<RT>),            // 0xfe00..05
+        Some(get_randomness::<RT>),           // 0xfe00..06
     ]);
 
     /// EVM specific precompiles
diff --git a/runtime/src/runtime/randomness.rs b/runtime/src/runtime/randomness.rs
index bb7d05d84..8283ad814 100644
--- a/runtime/src/runtime/randomness.rs
+++ b/runtime/src/runtime/randomness.rs
@@ -20,6 +20,7 @@ pub enum DomainSeparationTag {
     MarketDealCronSeed = 8,
     PoStChainCommit = 9,
     EvmPrevRandao = 10,
+    EvmRandPrecompile = 11,
 }
 
 #[allow(unused)]