diff --git a/packages/consensus/src/validation/block.cairo b/packages/consensus/src/validation/block.cairo
index 99d1259f..aad2d1cd 100644
--- a/packages/consensus/src/validation/block.cairo
+++ b/packages/consensus/src/validation/block.cairo
@@ -96,10 +96,10 @@ pub fn compute_and_validate_tx_data(
     validate_block_weight(total_weight)?;
 
     let wtxid_root = if block_height >= SEGWIT_BLOCK {
-        merkle_root(ref wtxids)
+        merkle_root(wtxids.span())
     } else {
         Zero::zero()
     };
 
-    Result::Ok((total_fee, merkle_root(ref txids), wtxid_root))
+    Result::Ok((total_fee, merkle_root(txids.span()), wtxid_root))
 }
diff --git a/packages/consensus/src/validation/coinbase.cairo b/packages/consensus/src/validation/coinbase.cairo
index 6c4bc1a4..416cc7f7 100644
--- a/packages/consensus/src/validation/coinbase.cairo
+++ b/packages/consensus/src/validation/coinbase.cairo
@@ -3,9 +3,7 @@
 //! https://learnmeabitcoin.com/technical/mining/coinbase-transaction/
 
 use crate::types::transaction::{Transaction, TxIn, TxOut};
-use utils::{
-    bit_shifts::shr, hash::{Digest, DigestIntoByteArray}, double_sha256::{double_sha256_byte_array}
-};
+use utils::{hash::{Digest, DigestIntoByteArray}, double_sha256::{double_sha256_byte_array}};
 
 const BIP_34_BLOCK_HEIGHT: u32 = 227_836;
 const BIP_141_BLOCK_HEIGHT: u32 = 481_824;
@@ -112,7 +110,13 @@ fn validate_coinbase_witness(witness: Span<ByteArray>) -> Result<(), ByteArray>
 
 /// Return BTC reward in SATS
 fn compute_block_reward(block_height: u32) -> u64 {
-    shr(5000000000_u64, (block_height / 210000_u32))
+    let mut result: u64 = 5_000_000_000;
+
+    for _ in 0..block_height / 210_000 {
+        result /= 2;
+    };
+
+    result
 }
 
 /// Calculate wtxid commitment
diff --git a/packages/utils/src/hex.cairo b/packages/utils/src/hex.cairo
index 736a403c..ef51e051 100644
--- a/packages/utils/src/hex.cairo
+++ b/packages/utils/src/hex.cairo
@@ -9,7 +9,7 @@ pub fn from_hex(hex_string: ByteArray) -> ByteArray {
     let mut bytes: ByteArray = Default::default();
     let mut i = 0;
 
-    while i < num_characters {
+    while i != num_characters {
         let hi = hex_char_to_nibble(hex_string[i]);
         let lo = hex_char_to_nibble(hex_string[i + 1]);
         bytes.append_byte(hi * 16 + lo);
@@ -25,10 +25,9 @@ pub fn to_hex(data: @ByteArray) -> ByteArray {
     let mut result: ByteArray = Default::default();
 
     let mut i = 0;
-    while i < data.len() {
-        let value = data[i];
-        let l: u32 = (value / 16).into();
-        let r: u32 = (value % 16).into();
+    while i != data.len() {
+        let value: u32 = data[i].into();
+        let (l, r) = core::traits::DivRem::div_rem(value, 16);
         result.append_byte(alphabet.at(l).unwrap());
         result.append_byte(alphabet.at(r).unwrap());
         i += 1;
@@ -39,16 +38,16 @@ pub fn to_hex(data: @ByteArray) -> ByteArray {
 // Get `Digest` form `ByteArray` reversed
 pub fn hex_to_hash_rev(hex_string: ByteArray) -> Digest {
     let mut result: Array<u32> = array![];
-    let mut i = 1;
+    let mut i = 0;
     let mut unit: u32 = 0;
     let len = hex_string.len();
-    while (i < len) {
-        if ((i - 1) % 8 == 0 && i - 1 > 0) {
+    while i != len {
+        if (i != 0 && i % 8 == 0) {
             result.append(unit);
             unit = 0;
         }
-        let hi = hex_char_to_nibble(hex_string[len - i - 1]);
-        let lo = hex_char_to_nibble(hex_string[len - i]);
+        let hi = hex_char_to_nibble(hex_string[len - i - 2]);
+        let lo = hex_char_to_nibble(hex_string[len - i - 1]);
         unit = (unit * 256) + (hi * 16 + lo).into();
         i += 2;
     };
diff --git a/packages/utils/src/merkle_tree.cairo b/packages/utils/src/merkle_tree.cairo
index f770939a..1df5d1e5 100644
--- a/packages/utils/src/merkle_tree.cairo
+++ b/packages/utils/src/merkle_tree.cairo
@@ -3,28 +3,31 @@
 use super::{double_sha256::double_sha256_parent, hash::Digest};
 
 /// Calculate Merkle tree root given the array of leaves.
-pub fn merkle_root(ref hashes: Array<Digest>) -> Digest {
+pub fn merkle_root(hashes: Span<Digest>) -> Digest {
     let len = hashes.len();
 
     if len == 1 {
         return *hashes[0];
     }
 
-    if len % 2 == 1 {
-        hashes.append(*hashes[len - 1]);
-    } else {
-        // CVE-2012-2459 bug fix
-        assert!(*hashes[len - 1] != *hashes[len - 2], "unexpected node duplication in merkle tree");
-    }
-
+    let (_, is_odd) = core::traits::DivRem::div_rem(len, 2);
+    let mut arr = hashes;
     let mut next_hashes: Array<Digest> = array![];
-    let mut i = 0;
-    while i < len {
-        next_hashes.append(double_sha256_parent(hashes[i], hashes[i + 1]));
-        i += 2;
+
+    while let Option::Some(v) = arr.multi_pop_front::<2>() {
+        let [a, b] = (*v).unbox();
+        next_hashes.append(double_sha256_parent(@a, @b));
     };
 
-    merkle_root(ref next_hashes)
+    if (is_odd == 1) {
+        let last = *arr.pop_front().unwrap();
+        next_hashes.append(double_sha256_parent(@last, @last));
+    } else if (*hashes[len - 1] == *hashes[len - 2]) {
+        // CVE-2012-2459 bug fix
+        panic!("unexpected node duplication in merkle tree");
+    }
+
+    merkle_root(next_hashes.span())
 }
 
 #[cfg(test)]
@@ -42,8 +45,7 @@ mod tests {
         let expected_merkle_root: Digest = hex_to_hash_rev(
             "acd9825be8bece7782ec746a80b52f44d6a8af41c63dbab59b03e29558469682"
         );
-
-        assert_eq!(merkle_root(ref txids), expected_merkle_root);
+        assert_eq!(merkle_root(txids.span()), expected_merkle_root);
     }
 
     #[test]
@@ -57,8 +59,7 @@ mod tests {
         let expected_merkle_root: Digest = hex_to_hash_rev(
             "7dac2c5666815c17a3b36427de37bb9d2e2c5ccec3f8633eb91a4205cb4c10ff"
         );
-
-        assert_eq!(merkle_root(ref txids), expected_merkle_root);
+        assert_eq!(merkle_root(txids.span()), expected_merkle_root);
     }
 
     #[test]
@@ -72,8 +73,7 @@ mod tests {
         let expected_merkle_root: Digest = hex_to_hash_rev(
             "035dff4bfc62ff255ddac842dd31be4d28756b3625b0c4fecade7011f8dada20"
         );
-
-        assert_eq!(merkle_root(ref txids), expected_merkle_root);
+        assert_eq!(merkle_root(txids.span()), expected_merkle_root);
     }
 
     #[test]
@@ -88,8 +88,7 @@ mod tests {
         let expected_merkle_root: Digest = hex_to_hash_rev(
             "222ae86adb1f65c0458f53f4c4c5d70966e12f122ef00bfdf2eac04022865013"
         );
-
-        assert_eq!(merkle_root(ref txids), expected_merkle_root);
+        assert_eq!(merkle_root(txids.span()), expected_merkle_root);
     }
 
     #[test]
@@ -105,8 +104,7 @@ mod tests {
         let expected_merkle_root = hex_to_hash_rev(
             "968bd407fe881936f5140e3794c85962db7e8614c1bb9894bb78b59e56be4555"
         );
-
-        assert_eq!(merkle_root(ref txids), expected_merkle_root);
+        assert_eq!(merkle_root(txids.span()), expected_merkle_root);
     }
 
     #[test]
@@ -136,8 +134,7 @@ mod tests {
         let expected_merkle_root: Digest = hex_to_hash_rev(
             "af77d9974359ae0699e62990b300d1e4663d03996176528bfa92aa24a65a45e1"
         );
-
-        assert_eq!(merkle_root(ref txids), expected_merkle_root);
+        assert_eq!(merkle_root(txids.span()), expected_merkle_root);
     }
 
     #[test]
@@ -183,7 +180,6 @@ mod tests {
         let expected_merkle_root: Digest = hex_to_hash_rev(
             "c78e335cb8908ecda32ff5dd44e9985099572692761f7809a400f60ec58d452c"
         );
-
-        assert_eq!(merkle_root(ref txids), expected_merkle_root);
+        assert_eq!(merkle_root(txids.span()), expected_merkle_root);
     }
 }
diff --git a/packages/utils/src/sha256.cairo b/packages/utils/src/sha256.cairo
index 8094a6a3..85af97d6 100644
--- a/packages/utils/src/sha256.cairo
+++ b/packages/utils/src/sha256.cairo
@@ -201,12 +201,12 @@ fn compression(w: Span<u32>, i: usize, k: Span<u32>, mut h: Span<u32>) -> Span<u
 fn create_message_schedule(data: Span<u32>, i: usize) -> Span<u32> {
     let mut j = 0;
     let mut result = array![];
-    while (j < 16) {
+    while (j != 16) {
         result.append(*data[i * 16 + j]);
         j += 1;
     };
     let mut i = 16;
-    while (i < 64) {
+    while (i != 64) {
         let s0 = ssig0(*result[i - 15]);
         let s1 = ssig1(*result[i - 2]);