added count_shared_prefix_len merkle util

src/library/merkle_patricia_utils.cairo

@@ -1,5 +1,5 @@
 use fossil::library::words64_utils::words64_to_nibbles;
-use fossil::types::Words64Sequence;
+use fossil::types::{Words64Sequence, Words64};
 
 pub fn merkle_patricia_input_decode(input: Words64Sequence) -> Array<u64> {
     let first_nibble = *words64_to_nibbles(input, 0).at(0);
@@ -23,6 +23,24 @@ pub fn merkle_patricia_input_decode(input: Words64Sequence) -> Array<u64> {
     words64_to_nibbles(input, skip_nibbles)
 }
 
+pub fn count_shared_prefix_len(
+    current_path_offset: usize, path: Words64, node_path: Words64, current_index: usize
+) -> usize {
+    if current_index + current_path_offset >= path.len() && current_index >= node_path.len() {
+        return current_index;
+    } else {
+        let path_nibble = *path.at(current_index + current_path_offset);
+        let node_path_nibble = *node_path.at(current_index);
+
+        if path_nibble == node_path_nibble {
+            return count_shared_prefix_len(current_path_offset, path, node_path, current_index + 1);
+        } else {
+            return current_index;
+        }
+
+    }
+}
+
 #[cfg(test)]
 mod tests {
     #[test]

src/types.cairo

@@ -1,4 +1,4 @@
-type Words64 = Span<u64>;
+pub type Words64 = Span<u64>;
 
 #[derive(Default, Drop, Serde, starknet::Store)]
 pub struct Keccak256Hash {