From 9687e42db45910a2da7035b8288f70001e373ba2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tom=C3=A1s?= <112426153+tomip01@users.noreply.github.com>
Date: Thu, 9 Jan 2025 16:13:41 -0300
Subject: [PATCH] fix(levm): for pre Berlin don't use floor cost modexp (#1675)

**Motivation**

This PR is for fixing the Ethereum Foundation Tests on the ModExp
precompile.

**Description**

When the `base_size` and `modulus_size` is Zero, there is an early
return to not make all the operations.
In the Berlin fork was introduced a floor for the gas cost. We were
returning this floor cost also for the previous forks to Berlin.
Now is only added after Berlin.
---
 crates/vm/levm/src/precompiles.rs | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/crates/vm/levm/src/precompiles.rs b/crates/vm/levm/src/precompiles.rs
index e9a36c6041..08ab64cd5c 100644
--- a/crates/vm/levm/src/precompiles.rs
+++ b/crates/vm/levm/src/precompiles.rs
@@ -306,7 +306,11 @@ pub fn modexp(
     );
 
     if base_size == U256::zero() && modulus_size == U256::zero() {
-        increase_precompile_consumed_gas(gas_for_call, MODEXP_STATIC_COST, consumed_gas)?;
+        // On Berlin or newer there is a floor cost for the modexp precompile
+        // On older versions in this return there is no cost added, see more https://eips.ethereum.org/EIPS/eip-2565
+        if spec_id >= SpecId::BERLIN {
+            increase_precompile_consumed_gas(gas_for_call, MODEXP_STATIC_COST, consumed_gas)?;
+        }
         return Ok(Bytes::new());
     }