Merge pull request #5 from lattice-based-cryptography/remove-floats

remove floats

src/decrypt.rs

@@ -1,6 +1,6 @@
 use polynomial_ring::Polynomial;
 use module_lwe::{Parameters,mul_vec_simple};
-use module_lwe::ring_mod::polysub;
+use module_lwe::ring_mod::{polysub,nearest_int};
 
 pub fn decrypt(
     sk: &Vec<Polynomial<i64>>,    //secret key
@@ -14,15 +14,11 @@ pub fn decrypt(
 
 	//Compute v-sk*u mod q
 	let scaled_pt = polysub(&v, &mul_vec_simple(&sk, &u, q, &f), q, &f);
-	let half_q = (q as f64 / 2.0 + 0.5) as i64;
+	let half_q = nearest_int(q,2);
 	let mut decrypted_coeffs = vec![];
 	let mut s;
 	for c in scaled_pt.coeffs().iter() {
-		if (half_q-c).abs() < std::cmp::min(*c, (q-c).abs()) {
-			s = 1;
-		} else {
-			s = 0;
-		};
+		s = nearest_int(*c,half_q) % 2;
 		decrypted_coeffs.push(s);
 	}
     decrypted_coeffs

src/encrypt.rs

@@ -1,5 +1,5 @@
 use polynomial_ring::Polynomial;
-use module_lwe::ring_mod::{polyadd,polysub};
+use module_lwe::ring_mod::{polyadd,polysub,nearest_int};
 use module_lwe::{Parameters, add_vec, mul_mat_vec_simple, transpose, mul_vec_simple, gen_small_vector};
 
 pub fn encrypt(
@@ -19,7 +19,7 @@ pub fn encrypt(
     let e2 = gen_small_vector(n, 1, seed)[0].clone(); // Single polynomial
 
     //compute nearest integer to q/2
-    let half_q = (q as f64 / 2.0 + 0.5) as i64;
+    let half_q = nearest_int(q,2);
 
     // Convert binary message to polynomial
     let m = Polynomial::new(vec![half_q])*Polynomial::new(m_b);

src/ring_mod.rs

@@ -83,4 +83,8 @@ pub fn gen_uniform_poly(size: usize, q: i64, seed: Option<u64>) -> Polynomial<i6
 		coeffs[i] = between.sample(&mut rng);
 	}
 	Polynomial::new(coeffs)
+}
+
+pub fn nearest_int(a: i64, b: i64) -> i64 {
+    (a + b / 2) / b
 }