From 5dc299372a742b2ba76302574c36ca2f6d5f9ad4 Mon Sep 17 00:00:00 2001
From: alivecow <mail@ta-lotz.de>
Date: Fri, 15 Nov 2024 10:13:05 +0100
Subject: [PATCH] fix: Add handling of zero mulitplication for polynomials

---
 src/utils/field.rs | 105 +++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 102 insertions(+), 3 deletions(-)

diff --git a/src/utils/field.rs b/src/utils/field.rs
index 14d0c46..758ea75 100644
--- a/src/utils/field.rs
+++ b/src/utils/field.rs
@@ -151,6 +151,15 @@ impl Polynomial {
 
         (Polynomial::new(quotient_coeffs), remainder)
     }
+
+    fn is_zero(&self) -> bool {
+        for field_element in &self.polynomial {
+            if !field_element.is_zero() {
+                return false;
+            }
+        }
+        true
+    }
 }
 
 impl Clone for Polynomial {
@@ -163,8 +172,10 @@ impl Clone for Polynomial {
 
 impl Mul for Polynomial {
     type Output = Self;
-
     fn mul(self, rhs: Self) -> Self::Output {
+        if self.is_zero() || rhs.is_zero() {
+            return Polynomial::new(vec![FieldElement::new(vec![0; 16])]);
+        }
         let mut polynomial: Vec<FieldElement> =
             vec![FieldElement::new(vec![0; 16]); self.polynomial.len() + rhs.polynomial.len() - 1];
         for i in 0..self.polynomial.len() {
@@ -180,6 +191,9 @@ impl Mul for Polynomial {
 impl Mul for &Polynomial {
     type Output = Polynomial;
     fn mul(self, rhs: Self) -> Self::Output {
+        if self.is_zero() || rhs.is_zero() {
+            return Polynomial::new(vec![FieldElement::new(vec![0])]);
+        }
         let mut polynomial: Vec<FieldElement> =
             vec![FieldElement::new(vec![0; 16]); self.polynomial.len() + rhs.polynomial.len() - 1];
         for i in 0..self.polynomial.len() {
@@ -296,6 +310,10 @@ impl FieldElement {
         //eprintln!("Inverse rhs {:?}", inverse);
         FieldElement::new(inverse)
     }
+
+    fn is_zero(&self) -> bool {
+        self.field_element.iter().all(|&x| x == 0x00)
+    }
 }
 
 impl Mul for FieldElement {
@@ -662,6 +680,68 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_field_add_zero() {
+        let json1 = json!([
+            "NeverGonnaGiveYouUpAAA==",
+            "NeverGonnaLetYouDownAA==",
+            "NeverGonnaRunAroundAAA==",
+            "AndDesertYouAAAAAAAAAA=="
+        ]);
+        let json2 = json!(["AAAAAAAAAAAAAAAAAAAAAA=="]);
+        let element1: Polynomial = Polynomial::from_c_array(&json1);
+        let element2: Polynomial = Polynomial::from_c_array(&json2);
+
+        let sum = element2 + element1;
+
+        assert_eq!(
+            sum.to_c_array(),
+            vec![
+                "NeverGonnaGiveYouUpAAA==",
+                "NeverGonnaLetYouDownAA==",
+                "NeverGonnaRunAroundAAA==",
+                "AndDesertYouAAAAAAAAAA=="
+            ]
+        );
+    }
+
+    #[test]
+    fn test_field_add_zero_to_zero() {
+        let json1 = json!(["AAAAAAAAAAAAAAAAAAAAAA=="]);
+        let json2 = json!(["AAAAAAAAAAAAAAAAAAAAAA=="]);
+        let element1: Polynomial = Polynomial::from_c_array(&json1);
+        let element2: Polynomial = Polynomial::from_c_array(&json2);
+
+        let sum = element2 + element1;
+
+        assert_eq!(sum.to_c_array(), vec!["AAAAAAAAAAAAAAAAAAAAAA=="]);
+    }
+
+    #[test]
+    fn test_field_add_short_to_long() {
+        let json1 = json!(["AAAAAAAAAAAAAAAAAAAAAA=="]);
+        let json2 = json!([
+            "NeverGonnaGiveYouUpAAA==",
+            "NeverGonnaLetYouDownAA==",
+            "NeverGonnaRunAroundAAA==",
+            "AndDesertYouAAAAAAAAAA=="
+        ]);
+        let element1: Polynomial = Polynomial::from_c_array(&json1);
+        let element2: Polynomial = Polynomial::from_c_array(&json2);
+
+        let sum = element2 + element1;
+
+        assert_eq!(
+            sum.to_c_array(),
+            vec![
+                "NeverGonnaGiveYouUpAAA==",
+                "NeverGonnaLetYouDownAA==",
+                "NeverGonnaRunAroundAAA==",
+                "AndDesertYouAAAAAAAAAA=="
+            ]
+        );
+    }
+
     #[test]
     fn test_field_mul_01() {
         let json1 = json!([
@@ -690,7 +770,26 @@ mod tests {
     }
 
     #[test]
-    fn test_field_pow_01() {
+    fn test_poly_mul_with_zero() {
+        let json1 = json!([
+            "JAAAAAAAAAAAAAAAAAAAAA==",
+            "wAAAAAAAAAAAAAAAAAAAAA==",
+            "ACAAAAAAAAAAAAAAAAAAAA=="
+        ]);
+        let json2 = json!(["AAAAAAAAAAAAAAAAAAAAAA=="]);
+        let element1: Polynomial = Polynomial::from_c_array(&json1);
+        let element2: Polynomial = Polynomial::from_c_array(&json2);
+
+        //eprintln!("{:?}", element1);
+
+        let result = element1 * element2;
+
+        assert_eq!(result.to_c_array(), vec!["AAAAAAAAAAAAAAAAAAAAAA=="]);
+        //assert_eq!(BASE64_STANDARD.encode(product), "MoAAAAAAAAAAAAAAAAAAAA==");
+    }
+
+    #[test]
+    fn test_poly_pow_01() {
         let json1 = json!([
             "JAAAAAAAAAAAAAAAAAAAAA==",
             "wAAAAAAAAAAAAAAAAAAAAA==",
@@ -792,6 +891,6 @@ mod tests {
         let result = element1.pow_mod(1000, modulus);
 
         eprintln!("Result is: {:02X?}", result);
-        assert_eq!(result.to_c_array(), vec!["XrEhmKuat+Glt5zZWtMo6g=="]);
+        assert_eq!(result.to_c_array(), vec!["oNXl5P8xq2WpUTP92u25zg=="]);
     }
 }