add more basic dot products and comments, README

Author: miguelraz

crates/core_simd/examples/README.md

@@ -0,0 +1,19 @@
+### `stdsimd` examples
+
+This crate is a port of example uses of `stdsimd`, mostly taken from the `packed_simd` crate.
+
+The examples contain, as in the case of `dot_product.rs`, multiple ways of solving the problem, in order to show idiomatic uses of SIMD and iteration of performance designs.
+
+Run the tests with the command 
+
+```
+cargo run --example dot_product
+```
+
+and the benchmarks via the command
+
+```
+cargo run --example --benchmark ???
+```
+
+and measure the timings on your local system.

crates/core_simd/examples/dot_product.rs

@@ -3,7 +3,27 @@
 #![feature(array_chunks)]
 use core_simd::*;
 
-pub fn dot_prod(a: &[f32], b: &[f32]) -> f32 {
+/// This is your barebones dot product implementation: 
+/// Take 2 vectors, multiply them element wise and *then*
+/// add up the result. In the next example we will see if there
+///  is any difference to adding as we go along multiplying.
+pub fn dot_prod_0(a: &[f32], b: &[f32]) -> f32 {
+    assert_eq!(a.len(), b.len());
+
+    a.iter()
+    .zip(b.iter())
+    .map(|a, b| a * b)
+    .sum()
+}
+
+pub fn dot_prod_1(a: &[f32], b: &[f32]) -> f32 {
+    assert_eq!(a.len(), b.len());
+    a.iter()
+    .zip(b.iter())
+    .fold(0.0, |a, b| a * b)
+}
+
+pub fn dot_prod_simd_0(a: &[f32], b: &[f32]) -> f32 {
     assert_eq!(a.len(), b.len());
 
     // TODO handle remainder when a.len() % 4 != 0
@@ -21,11 +41,14 @@ fn main() {
 #[cfg(test)]
 mod tests {
     #[test]
-    fn test() {
+    fn smoke_test() {
         use super::*;
         let a: Vec<f32> = vec![1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0];
         let b: Vec<f32> = vec![-8.0, -7.0, -6.0, -5.0, 4.0, 3.0, 2.0, 1.0];
 
-        assert_eq!(0.0, dot_prod(&a, &b));
+        assert_eq!(0.0, dot_prod_0(&a, &b));
+        assert_eq!(0.0, dot_prod_1(&a, &b));
+        assert_eq!(0.0, dot_prod_simd_0(&a, &b));
+        assert_eq!(0.0, dot_prod_simd_1(&a, &b));
     }
 }