From 4b4436e551ce06446fff154547736925b4212624 Mon Sep 17 00:00:00 2001
From: DaniPopes <57450786+DaniPopes@users.noreply.github.com>
Date: Sat, 15 Jun 2024 11:44:18 +0200
Subject: [PATCH] chore: simplify algorithms::mul*

---
 src/algorithms/mul.rs | 61 +++++++++++++++++--------------------------
 1 file changed, 24 insertions(+), 37 deletions(-)

diff --git a/src/algorithms/mul.rs b/src/algorithms/mul.rs
index 2c5436e..16e47a8 100644
--- a/src/algorithms/mul.rs
+++ b/src/algorithms/mul.rs
@@ -122,9 +122,7 @@ pub fn add_nx1(lhs: &mut [u64], mut a: u64) -> u64 {
         return 0;
     }
     for lhs in lhs {
-        let sum = u128::add(*lhs, a);
-        *lhs = sum.low();
-        a = sum.high();
+        (*lhs, a) = u128::add(*lhs, a).split();
         if a == 0 {
             return 0;
         }
@@ -147,18 +145,16 @@ pub fn addmul_n(lhs: &mut [u64], a: &[u64], b: &[u64]) {
         2 => addmul_2(lhs, a, b),
         3 => addmul_3(lhs, a, b),
         4 => addmul_4(lhs, a, b),
-        _ => {
-            let _ = addmul(lhs, a, b);
-        }
+        _ => _ = addmul(lhs, a, b),
     }
 }
 
 /// Computes `lhs += a * b` for 1 limb.
 #[inline(always)]
 fn addmul_1(lhs: &mut [u64], a: &[u64], b: &[u64]) {
-    assert_eq!(lhs.len(), 1);
-    assert_eq!(a.len(), 1);
-    assert_eq!(b.len(), 1);
+    assume!(lhs.len() == 1);
+    assume!(a.len() == 1);
+    assume!(b.len() == 1);
 
     mac(&mut lhs[0], a[0], b[0], 0);
 }
@@ -166,9 +162,9 @@ fn addmul_1(lhs: &mut [u64], a: &[u64], b: &[u64]) {
 /// Computes `lhs += a * b` for 2 limbs.
 #[inline(always)]
 fn addmul_2(lhs: &mut [u64], a: &[u64], b: &[u64]) {
-    assert_eq!(lhs.len(), 2);
-    assert_eq!(a.len(), 2);
-    assert_eq!(b.len(), 2);
+    assume!(lhs.len() == 2);
+    assume!(a.len() == 2);
+    assume!(b.len() == 2);
 
     let carry = mac(&mut lhs[0], a[0], b[0], 0);
     mac(&mut lhs[1], a[0], b[1], carry);
@@ -179,9 +175,9 @@ fn addmul_2(lhs: &mut [u64], a: &[u64], b: &[u64]) {
 /// Computes `lhs += a * b` for 3 limbs.
 #[inline(always)]
 fn addmul_3(lhs: &mut [u64], a: &[u64], b: &[u64]) {
-    assert_eq!(lhs.len(), 3);
-    assert_eq!(a.len(), 3);
-    assert_eq!(b.len(), 3);
+    assume!(lhs.len() == 3);
+    assume!(a.len() == 3);
+    assume!(b.len() == 3);
 
     let carry = mac(&mut lhs[0], a[0], b[0], 0);
     let carry = mac(&mut lhs[1], a[0], b[1], carry);
@@ -196,9 +192,9 @@ fn addmul_3(lhs: &mut [u64], a: &[u64], b: &[u64]) {
 /// Computes `lhs += a * b` for 4 limbs.
 #[inline(always)]
 fn addmul_4(lhs: &mut [u64], a: &[u64], b: &[u64]) {
-    assert_eq!(lhs.len(), 4);
-    assert_eq!(a.len(), 4);
-    assert_eq!(b.len(), 4);
+    assume!(lhs.len() == 4);
+    assume!(a.len() == 4);
+    assume!(b.len() == 4);
 
     let carry = mac(&mut lhs[0], a[0], b[0], 0);
     let carry = mac(&mut lhs[1], a[0], b[1], carry);
@@ -226,10 +222,8 @@ fn mac(lhs: &mut u64, a: u64, b: u64, c: u64) -> u64 {
 #[inline]
 pub fn mul_nx1(lhs: &mut [u64], a: u64) -> u64 {
     let mut carry = 0;
-    for lhs in &mut *lhs {
-        let product = u128::muladd(*lhs, a, carry);
-        *lhs = product.low();
-        carry = product.high();
+    for lhs in lhs {
+        (*lhs, carry) = u128::muladd(*lhs, a, carry).split();
     }
     carry
 }
@@ -246,12 +240,10 @@ pub fn mul_nx1(lhs: &mut [u64], a: u64) -> u64 {
 /// $$
 #[inline]
 pub fn addmul_nx1(lhs: &mut [u64], a: &[u64], b: u64) -> u64 {
-    debug_assert_eq!(lhs.len(), a.len());
+    assume!(lhs.len() == a.len());
     let mut carry = 0;
-    for (lhs, a) in lhs.iter_mut().zip(a.iter().copied()) {
-        let product = u128::muladd2(a, b, carry, *lhs);
-        *lhs = product.low();
-        carry = product.high();
+    for i in 0..a.len() {
+        (lhs[i], carry) = u128::muladd2(a[i], b, carry, lhs[i]).split();
     }
     carry
 }
@@ -269,21 +261,16 @@ pub fn addmul_nx1(lhs: &mut [u64], a: &[u64], b: u64) -> u64 {
 // OPT: `carry` and `borrow` can probably be merged into a single var.
 #[inline]
 pub fn submul_nx1(lhs: &mut [u64], a: &[u64], b: u64) -> u64 {
-    debug_assert_eq!(lhs.len(), a.len());
+    assume!(lhs.len() == a.len());
     let mut carry = 0;
     let mut borrow = 0;
-    for (lhs, a) in lhs.iter_mut().zip(a.iter().copied()) {
+    for i in 0..a.len() {
         // Compute product limbs
-        let limb = {
-            let product = u128::muladd(a, b, carry);
-            carry = product.high();
-            product.low()
-        };
+        let limb;
+        (limb, carry) = u128::muladd(a[i], b, carry).split();
 
         // Subtract
-        let (new, b) = sbb(*lhs, limb, borrow);
-        *lhs = new;
-        borrow = b;
+        (lhs[i], borrow) = sbb(lhs[i], limb, borrow);
     }
     borrow + carry
 }