From 053ed0fd68118b72c7eb9d6abfbd35bb45caba0a Mon Sep 17 00:00:00 2001
From: Pedro Fontana <fontana.pedro93@gmail.com>
Date: Mon, 11 Dec 2023 15:43:07 -0300
Subject: [PATCH] Implement felt to bigint functions

---
 crates/starknet-types-core/Cargo.toml  |  1 +
 crates/starknet-types-core/src/felt.rs | 41 ++++++++++++++++++++++++++
 2 files changed, 42 insertions(+)

diff --git a/crates/starknet-types-core/Cargo.toml b/crates/starknet-types-core/Cargo.toml
index 1b61b80..e6b9d39 100644
--- a/crates/starknet-types-core/Cargo.toml
+++ b/crates/starknet-types-core/Cargo.toml
@@ -21,6 +21,7 @@ arbitrary = { version = "1.3.0", optional = true, default-features = false }
 num-traits = { version = "0.2.16", default-features = false }
 num-bigint = {version = "0.4.4",  default-features = false}
 num-integer = {version = "0.1.45",  default-features = false}
+lazy_static = { version = "1.4.0", default-features = false }
 
 [features]
 default = ["std", "serde", "curve"]
diff --git a/crates/starknet-types-core/src/felt.rs b/crates/starknet-types-core/src/felt.rs
index 86a905d..b96bebf 100644
--- a/crates/starknet-types-core/src/felt.rs
+++ b/crates/starknet-types-core/src/felt.rs
@@ -945,6 +945,47 @@ mod errors {
     }
 }
 
+pub mod bigints {
+    use lazy_static::lazy_static;
+    use num_bigint::{BigUint, Sign, ToBigInt};
+    use num_traits::Num;
+
+    use super::*;
+    lazy_static! {
+        pub static ref CAIRO_PRIME_BIGINT: BigInt = BigInt::from_str_radix(
+            "800000000000011000000000000000000000000000000000000000000000001",
+            16
+        )
+        .unwrap();
+    }
+
+    pub fn felt_to_biguint(felt: Felt) -> BigUint {
+        let big_digits = felt
+            .to_le_digits()
+            .into_iter()
+            .flat_map(|limb| [limb as u32, (limb >> 32) as u32])
+            .collect();
+        BigUint::new(big_digits)
+    }
+
+    pub fn felt_to_bigint(felt: Felt) -> BigInt {
+        felt_to_biguint(felt).to_bigint().unwrap()
+    }
+
+    pub fn biguint_to_felt(biguint: &BigUint) -> Felt {
+        Felt::from_bytes_le_slice(&biguint.to_bytes_le())
+    }
+
+    pub fn bigint_to_felt(bigint: &BigInt) -> Felt {
+        let (sign, bytes) = bigint.mod_floor(&CAIRO_PRIME_BIGINT).to_bytes_le();
+        let felt = Felt::from_bytes_le_slice(&bytes);
+        if sign == Sign::Minus {
+            felt.neg()
+        } else {
+            felt
+        }
+    }
+}
 #[cfg(test)]
 mod test {
     use super::alloc::{format, string::String, vec::Vec};