Catch possible subtraction error in QUAD_BIT & DI_BIT hints (#1185)

* Catch possible sustraction error in QUAD_BIT & DI_BIT hints

* Fix changelog entry

* Typo

* Fix changelog entry

Author: fmoletta

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 #### Upcoming Changes
 
+* Fix possible subtraction overflow in `QUAD_BIT` & `DI_BIT` hints [#1185](https://github.com/lambdaclass/cairo-rs/pull/1185)
+
+  * These hints now return an error when ids.m equals zero
+
 * Add `CairoRunner::run_until_pc_with_steps_limit method` [#1181](https://github.com/lambdaclass/cairo-rs/pull/1181)
 
 * fix: felt_from_number not properly returning parse errors [#1012](https://github.com/lambdaclass/cairo-rs/pull/1012)

src/hint_processor/builtin_hint_processor/secp/ec_utils.rs

@@ -487,6 +487,9 @@ pub fn n_pair_bits(
     if m >= 253 {
         return insert_value_from_var_name("quad_bit", 0, vm, ids_data, ap_tracking);
     }
+    if m.is_zero() {
+        return Err(HintError::NPairBitsMZero);
+    }
 
     let one = &Felt252::one();
     let two = &Felt252::from(2);
@@ -1281,6 +1284,29 @@ mod tests {
         check_memory![vm.segments.memory, ((1, 3), 2)];
     }
 
+    #[test]
+    fn run_di_bit_m_zero() {
+        let hint_code = hint_code::DI_BIT;
+        let mut vm = vm_with_range_check!();
+
+        let scalar_u = 0b10101111001110000;
+        let scalar_v = 0b101101000111011111100;
+        let m = 0;
+        // Insert ids.scalar into memory
+        vm.segments = segments![((1, 0), scalar_u), ((1, 1), scalar_v), ((1, 2), m)];
+
+        // Initialize RunContext
+        run_context!(vm, 0, 4, 4);
+
+        let ids_data = ids_data!["scalar_u", "scalar_v", "m", "dibit"];
+
+        // Execute the hint
+        assert_matches!(
+            run_hint!(vm, ids_data, hint_code),
+            Err(HintError::NPairBitsMZero)
+        );
+    }
+
     #[test]
     #[cfg_attr(target_arch = "wasm32", wasm_bindgen_test)]
     fn run_import_secp256r1_alpha() {

src/vm/errors/hint_errors.rs

@@ -179,4 +179,6 @@ pub enum HintError {
     RecoverYPointNotOnCurve(Felt252),
     #[error("Invalid value for {0}. Got: {1}. Expected: {2}")]
     InvalidValue(&'static str, Felt252, Felt252),
+    #[error("Attempt to subtract with overflow: ids.m - 1")]
+    NPairBitsMZero,
 }