From 79c7c4a1836f60e56098c5f5db0c934169c1024f Mon Sep 17 00:00:00 2001
From: Eirik Ogilvie-Wigley <eirik@z.cash>
Date: Thu, 6 Sep 2018 10:54:41 -0600
Subject: [PATCH] Use existing utility functions

---
 src/fq.rs | 66 +++++++++++++++++++------------------------------------
 1 file changed, 23 insertions(+), 43 deletions(-)

diff --git a/src/fq.rs b/src/fq.rs
index b86af28..8b2dd27 100644
--- a/src/fq.rs
+++ b/src/fq.rs
@@ -72,6 +72,13 @@ fn adc2(a: u64, b: u64, carry: u64) -> (u64, u64) {
     (adc as u64, (adc >> 64) as u64)
 }
 
+/// Compute a + b, returning the result and the carry over.
+#[inline(always)]
+fn overflowing_add(a: u64, b: u64) -> (u64, u64) {
+    let (sum, overflow) = a.overflowing_add(b);
+    (sum, overflow as u64)
+}
+
 /// Compute a - (b + borrow), returning the result and setting borrow to
 /// the borrow value.
 #[inline(always)]
@@ -262,42 +269,16 @@ impl Fq {
         res
     }
     
-    /// Calculate a + (b * c) + carry, returning the least significant digit
-    /// and setting carry to the most significant digit.
-    #[inline(always)]
-    fn mac_with_carry(a: u64, b: u64, c: u64, carry: &mut u64) -> u64 {
-        let tmp = (u128::from(a)) + u128::from(b) * u128::from(c) + u128::from(*carry);
-
-        *carry = (tmp >> 64) as u64;
-
-        tmp as u64
-    }
-
-    /// Calculate a + b + carry, returning the sum and modifying the
-    /// carry value.
-    #[inline(always)]
-    fn adc(a: u64, b: u64, carry: &mut u64) -> u64 {
-        let tmp = u128::from(a) + u128::from(b) + u128::from(*carry);
-
-        *carry = (tmp >> 64) as u64;
-
-        tmp as u64
-    }
-
     /// Squares this element.
     pub fn square_assign(&mut self) {
-        let mut carry = 0;
-        let r1 = Fq::mac_with_carry(0, self.0[0], self.0[1], &mut carry);
-        let r2 = Fq::mac_with_carry(0, self.0[0], self.0[2], &mut carry);
-        let r3 = Fq::mac_with_carry(0, self.0[0], self.0[3], &mut carry);
-        let r4 = carry;
-        let mut carry = 0;
-        let r3 = Fq::mac_with_carry(r3, self.0[1], self.0[2], &mut carry);
-        let r4 = Fq::mac_with_carry(r4, self.0[1], self.0[3], &mut carry);
-        let r5 = carry;
-        let mut carry = 0;
-        let r5 = Fq::mac_with_carry(r5, self.0[2], self.0[3], &mut carry);
-        let r6 = carry;
+        let (r1, carry) = overflowing_mul(self.0[0], self.0[1]);
+        let (r2, carry) = mac(carry, self.0[0], self.0[2]);
+        let (r3, r4) = mac(carry, self.0[0], self.0[3]);
+
+        let (r3, carry) = mac(r3, self.0[1], self.0[2]);
+        let (r4, r5) = mac_with_carry(r4, self.0[1], self.0[3], carry);
+
+        let (r5, r6) = mac(r5, self.0[2], self.0[3]);
 
         let r7 = r6 >> 63;
         let r6 = (r6 << 1) | (r5 >> 63);
@@ -307,15 +288,14 @@ impl Fq {
         let r2 = (r2 << 1) | (r1 >> 63);
         let r1 = r1 << 1;
 
-        let mut carry = 0;
-        let r0 = Fq::mac_with_carry(0, self.0[0], self.0[0], &mut carry);
-        let r1 = Fq::adc(r1, 0, &mut carry);
-        let r2 = Fq::mac_with_carry(r2, self.0[1], self.0[1], &mut carry);
-        let r3 = Fq::adc(r3, 0, &mut carry);
-        let r4 = Fq::mac_with_carry(r4, self.0[2], self.0[2], &mut carry);
-        let r5 = Fq::adc(r5, 0, &mut carry);
-        let r6 = Fq::mac_with_carry(r6, self.0[3], self.0[3], &mut carry);
-        let r7 = Fq::adc(r7, 0, &mut carry);
+        let (r0, carry) = overflowing_mul(self.0[0], self.0[0]);
+        let (r1, carry) = overflowing_add(r1, carry);
+        let (r2, carry) = mac_with_carry(r2, self.0[1], self.0[1], carry);
+        let (r3, carry) = overflowing_add(r3, carry);
+        let (r4, carry) = mac_with_carry(r4, self.0[2], self.0[2], carry);
+        let (r5, carry) = overflowing_add(r5, carry);
+        let (r6, carry) = mac_with_carry(r6, self.0[3], self.0[3], carry);
+        let r7 = r7 + carry;
 
         self.montgomery_reduce(r0, r1, r2, r3, r4, r5, r6, r7);
     }