perf(l1): improve ecrecover by removing needless alloc and conversion (#5738)

**Motivation**

Removed a vec alloc and a U256 conversion that could be avoided

Tried to run the benchmarks but unrelated things improve and regress, so
i think its a bit flaky, this PR only changed the precompile function so
its hard to imagine how it affects that

Author: edg-l

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Perf
 
+### 2026-01-13
+
+- Improve ecrecover precompile by removing heap allocs and conversions [#5709](https://github.com/lambdaclass/ethrex/pull/5709)
+
 ### 2026-01-12
 
 - Refactor `ecpairing` using ark [#5792](https://github.com/lambdaclass/ethrex/pull/5792)

crates/vm/levm/src/precompiles.rs

@@ -375,6 +375,23 @@ pub(crate) fn fill_with_zeros(calldata: &Bytes, target_len: usize) -> Bytes {
     padded_calldata.into()
 }
 
+#[expect(clippy::arithmetic_side_effects, clippy::indexing_slicing)]
+#[cfg(all(
+    not(feature = "sp1"),
+    not(feature = "risc0"),
+    not(feature = "zisk"),
+    feature = "secp256k1"
+))]
+#[inline(always)]
+fn copy_segment(calldata: &Bytes, dst: &mut [u8], start: usize) {
+    if start >= calldata.len() {
+        return;
+    }
+    let end = (start + dst.len()).min(calldata.len());
+    let src = &calldata[start..end];
+    dst[..src.len()].copy_from_slice(src);
+}
+
 #[cfg(all(
     not(feature = "sp1"),
     not(feature = "risc0"),
@@ -386,19 +403,25 @@ pub fn ecrecover(calldata: &Bytes, gas_remaining: &mut u64, _fork: Fork) -> Resu
 
     increase_precompile_consumed_gas(ECRECOVER_COST, gas_remaining)?;
 
-    const INPUT_LEN: usize = 128;
     const WORD: usize = 32;
+    const SIG_LEN: usize = 64;
 
-    let input = fill_with_zeros(calldata, INPUT_LEN);
+    // Total input size = 128
+    let mut raw_hash = [0u8; WORD];
+    let mut raw_v = [0u8; WORD];
+    let mut raw_sig = [0u8; SIG_LEN];
 
-    // len(raw_hash) == 32, len(raw_v) == 32, len(raw_sig) == 64
-    let (raw_hash, tail) = input.split_at(WORD);
-    let (raw_v, raw_sig) = tail.split_at(WORD);
+    copy_segment(calldata, &mut raw_hash, 0);
+    copy_segment(calldata, &mut raw_v, WORD);
+    copy_segment(calldata, &mut raw_sig, WORD * 2);
 
     // EVM expects v ∈ {27, 28}. Anything else is invalid → empty return.
-    let recovery_id_byte = match u8::try_from(u256_from_big_endian(raw_v)) {
-        Ok(27) => 0_i32,
-        Ok(28) => 1_i32,
+    if raw_v[..(WORD - 1)].iter().any(|&b| b != 0) {
+        return Ok(Bytes::new());
+    }
+    let recovery_id_byte = match raw_v[WORD - 1] {
+        27 => 0_i32,
+        28 => 1_i32,
         _ => return Ok(Bytes::new()),
     };
 
@@ -408,16 +431,12 @@ pub fn ecrecover(calldata: &Bytes, gas_remaining: &mut u64, _fork: Fork) -> Resu
     };
 
     let Ok(recoverable_signature) =
-        secp256k1::ecdsa::RecoverableSignature::from_compact(raw_sig, recovery_id)
+        secp256k1::ecdsa::RecoverableSignature::from_compact(&raw_sig, recovery_id)
     else {
         return Ok(Bytes::new());
     };
 
-    let message = secp256k1::Message::from_digest(
-        raw_hash
-            .try_into()
-            .map_err(|_err| InternalError::msg("Invalid message length for ecrecover"))?,
-    );
+    let message = secp256k1::Message::from_digest(raw_hash);
 
     let Ok(public_key) = recoverable_signature.recover(&message) else {
         return Ok(Bytes::new());