allocating fold with std::ops::Add::add

Author: miguelraz

crates/core_simd/examples/dot_product.rs

@@ -112,34 +112,31 @@ pub fn dot_prod_simd_3(a: &[f32], b: &[f32]) -> f32 {
 // Finally, we present an iterator version for handling remainders in a scalar fashion at the end of the loop.
 // Unfortunately, this is allocating 1 `XMM` register on the order of `~len(a)` - we'll see how we can get around it in the
 // next example.
-use std::ops::Add;
 pub fn dot_prod_simd_4(a: &[f32], b: &[f32]) -> f32 {
     let mut sum = a
         .array_chunks::<4>()
         .map(|&a| f32x4::from_array(a))
         .zip(b.array_chunks::<4>().map(|&b| f32x4::from_array(b)))
         .map(|(a, b)| a * b)
-        .fold(f32x4::splat(0.), std::ops::Add)
+        .fold(f32x4::splat(0.0), std::ops::Add::add)
         .reduce_sum();
     let remain = a.len() - (a.len() % 4);
     sum += a[remain..]
         .iter()
         .zip(&b[remain..])
         .map(|(a, b)| a * b)
-        .sum();
+        .sum::<f32>();
     sum
 }
 
 // This version allocates a single `XMM` register for accumulation, and the folds don't allocate on top of that.
 // Notice the the use of `mul_add`, which can do a multiply and an add operation ber iteration.
 pub fn dot_prod_simd_5(a: &[f32], b: &[f32]) -> f32 {
-    let mut sum = a
-        .array_chunks::<4>()
+    a.array_chunks::<4>()
         .map(|&a| f32x4::from_array(a))
         .zip(b.array_chunks::<4>().map(|&b| f32x4::from_array(b)))
         .fold(f32x4::splat(0.), |acc, (a, b)| acc.mul_add(a, b))
-        .reduce_sum();
-    sum
+        .reduce_sum()
 }
 
 fn main() {