bugfix: Fix hint BIGINT_PACK_DIV_MOD (lambdaclass#1189)

* Use `to_signed_felt` instead of `to_bigint`

* fmt

* Add changelog entry

Author: fmoletta

CHANGELOG.md

@@ -2,9 +2,11 @@
 
 #### Upcoming Changes
 
-* bugfix: Fix `EC_DOUBLE_ASSIGN_NEW_X_V2` hint not taking `SECP_P` value from the current execution scope [#1186](https://github.com/lambdaclass/cairo-rs/pull/1186)
+* fix: Fix hint `BIGINT_PACK_DIV_MOD` [#1189](https://github.com/lambdaclass/cairo-rs/pull/1189)
 
-* Fix possible subtraction overflow in `QUAD_BIT` & `DI_BIT` hints [#1185](https://github.com/lambdaclass/cairo-rs/pull/1185)
+* fix: Fix `EC_DOUBLE_ASSIGN_NEW_X_V2` hint not taking `SECP_P` value from the current execution scope [#1186](https://github.com/lambdaclass/cairo-rs/pull/1186)
+
+* fix: 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
 

src/hint_processor/builtin_hint_processor/bigint.rs

@@ -14,7 +14,6 @@ use crate::{
 };
 use felt::Felt252;
 use num_bigint::BigInt;
-use num_bigint::ToBigInt;
 use num_traits::{One, Signed, Zero};
 
 use super::hint_utils::insert_value_from_var_name;
@@ -37,27 +36,22 @@ pub fn bigint_pack_div_mod_hint(
     ids_data: &HashMap<String, HintReference>,
     ap_tracking: &ApTracking,
 ) -> Result<(), HintError> {
-    let p: BigInt = BigInt3::from_var_name("P", vm, ids_data, ap_tracking)?
-        .pack86()
-        .to_bigint()
-        .unwrap_or_default();
+    let p: BigInt = BigInt3::from_var_name("P", vm, ids_data, ap_tracking)?.pack86();
 
     let x: BigInt = {
         let x_bigint5 = BigInt5::from_var_name("x", vm, ids_data, ap_tracking)?;
+        // pack only takes the first three limbs
         let x_lower = BigInt3 {
             d0: x_bigint5.d0,
             d1: x_bigint5.d1,
             d2: x_bigint5.d2,
         };
-        let x_lower = x_lower.pack86().to_bigint().unwrap_or_default();
-        let d3 = x_bigint5.d3.as_ref().to_bigint();
-        let d4 = x_bigint5.d4.as_ref().to_bigint();
+        let x_lower = x_lower.pack86();
+        let d3 = x_bigint5.d3.as_ref().to_signed_felt();
+        let d4 = x_bigint5.d4.as_ref().to_signed_felt();
         x_lower + d3 * BigInt::from(BASE.pow(3)) + d4 * BigInt::from(BASE.pow(4))
     };
-    let y: BigInt = BigInt3::from_var_name("y", vm, ids_data, ap_tracking)?
-        .pack86()
-        .to_bigint()
-        .unwrap_or_default();
+    let y: BigInt = BigInt3::from_var_name("y", vm, ids_data, ap_tracking)?.pack86();
 
     let res = div_mod(&x, &y, &p);
     exec_scopes.insert_value("res", res.clone());