From 5e48450d7f8c7adfb0c106049fe265bc1c3b8b39 Mon Sep 17 00:00:00 2001
From: Bartosz Nowak <bartekn337@gmail.com>
Date: Thu, 24 Oct 2024 13:49:11 +0200
Subject: [PATCH] impl missing hint

---
 .../src/hints/lib/rlp_little/leading_zeros.rs | 32 +++++++++++++++++++
 lib/rlp_little.cairo                          |  2 +-
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/cairo_vm_hints/src/hints/lib/rlp_little/leading_zeros.rs b/cairo_vm_hints/src/hints/lib/rlp_little/leading_zeros.rs
index dd19d6c..99c4a21 100644
--- a/cairo_vm_hints/src/hints/lib/rlp_little/leading_zeros.rs
+++ b/cairo_vm_hints/src/hints/lib/rlp_little/leading_zeros.rs
@@ -41,3 +41,35 @@ pub fn hint_expected_leading_zeroes(
 
     Ok(())
 }
+
+pub const HINT_EXPECTED_NIBBLE: &str = "key_hex = ids.key_leading_zeroes_nibbles * '0' + hex(ids.key.low + (2 ** 128) * ids.key.high)[2:]\nexpected_nibble = int(key_hex[ids.nibble_index + ids.key_leading_zeroes_nibbles], 16)";
+
+pub fn hint_expected_nibble(
+    vm: &mut VirtualMachine,
+    exec_scope: &mut ExecutionScopes,
+    hint_data: &HintProcessorData,
+    _constants: &HashMap<String, Felt252>,
+) -> Result<(), HintError> {
+    let key_low: u128 = utils::get_value("key.low", vm, hint_data)?
+        .try_into()
+        .unwrap();
+    let key_high: u128 = utils::get_value("key.high", vm, hint_data)?
+        .try_into()
+        .unwrap();
+    let key_leading_zeroes_nibbles: usize =
+        utils::get_value("key_leading_zeroes_nibbles", vm, hint_data)?
+            .try_into()
+            .unwrap();
+    let nibble_index: usize = utils::get_value("nibble_index", vm, hint_data)?
+        .try_into()
+        .unwrap();
+
+    let hex = hex::encode([key_low.to_be_bytes(), key_high.to_be_bytes()].concat());
+    let nibble_char = format!("{:0width$}{}", "", hex, width = key_leading_zeroes_nibbles)
+        .chars()
+        .nth(nibble_index + key_leading_zeroes_nibbles)
+        .unwrap();
+    exec_scope.insert_value("expected_nibble", nibble_char.to_digit(16).unwrap());
+
+    Ok(())
+}
diff --git a/lib/rlp_little.cairo b/lib/rlp_little.cairo
index 81dd7a6..eedd608 100644
--- a/lib/rlp_little.cairo
+++ b/lib/rlp_little.cairo
@@ -421,7 +421,7 @@ func extract_nibble_from_key_be{range_check_ptr, bitwise_ptr: BitwiseBuiltin*}(
         //      print(f"key_nibbles: {ids.key_nibbles}")
         //      print(f"key_leading_zeroes_nibbles: {ids.key_leading_zeroes_nibbles}")
         // %}
-        %{ //TODO
+        %{
             key_hex = ids.key_leading_zeroes_nibbles * '0' + hex(ids.key.low + (2 ** 128) * ids.key.high)[2:]
             expected_nibble = int(key_hex[ids.nibble_index + ids.key_leading_zeroes_nibbles], 16)
         %}