add dot_product example

crates/core_simd/examples/dot_product.rs

@@ -0,0 +1,31 @@
+// Code taken from the `packed_simd` crate
+// Run this code with `cargo test --example dot_product`
+#![feature(array_chunks)]
+use core_simd::*;
+
+pub fn dot_prod(a: &[f32], b: &[f32]) -> f32 {
+    assert_eq!(a.len(), b.len());
+
+    // TODO handle remainder when a.len() % 4 != 0
+    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).horizontal_sum())
+        .sum()
+}
+
+fn main() {
+    // Empty main to make cargo happy
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn 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));
+    }
+}