Move to the hgg crate

milli/src/distance.rs

@@ -0,0 +1,34 @@
+use serde::{Deserialize, Serialize};
+use space::Metric;
+
+#[derive(Debug, Default, Clone, Copy, Serialize, Deserialize)]
+pub struct DotProduct;
+
+impl Metric<Vec<f32>> for DotProduct {
+    type Unit = u32;
+
+    // TODO explain me this function, I don't understand why f32.to_bits is ordered.
+    // I tried to do this and it wasn't OK <https://stackoverflow.com/a/43305015/1941280>
+    //
+    // Following <https://docs.rs/space/0.17.0/space/trait.Metric.html>.
+    fn distance(&self, a: &Vec<f32>, b: &Vec<f32>) -> Self::Unit {
+        let dist: f32 = a.iter().zip(b).map(|(a, b)| a * b).sum();
+        let dist = 1.0 - dist;
+        debug_assert!(!dist.is_nan());
+        dist.to_bits()
+    }
+}
+
+#[derive(Debug, Default, Clone, Copy, Serialize, Deserialize)]
+pub struct Euclidean;
+
+impl Metric<Vec<f32>> for Euclidean {
+    type Unit = u32;
+
+    fn distance(&self, a: &Vec<f32>, b: &Vec<f32>) -> Self::Unit {
+        let squared: f32 = a.iter().zip(b).map(|(a, b)| (a - b).powi(2)).sum();
+        let dist = squared.sqrt();
+        debug_assert!(!dist.is_nan());
+        dist.to_bits()
+    }
+}