Changes:

- added `Historgram` struct
- added function `cos_sim`

src/lib.rs

@@ -2,6 +2,7 @@ extern crate core;
 
 pub mod image;
 pub mod multithreading;
+pub mod stdfeats;
 
 pub fn add(left: usize, right: usize) -> usize {
     left + right

src/stdfeats/historgram.rs

@@ -0,0 +1,44 @@
+use std::sync::Arc;
+
+use serde::{Serialize, Deserialize};
+
+use crate::image::Image;
+
+#[derive(Debug, Serialize, Deserialize)]
+pub struct Histogram {
+    // vector of buckets in the histogram
+    buckets: Vec<(f32, f32, f32, f32)>,
+    // count elements in the buckets from the histogram
+    count: Vec<f32>
+}
+
+impl Histogram {
+
+    pub fn map_image<T>(&mut self, image: &Arc<Image<T>>) where T: Default + Copy + From<u8> + std::cmp::PartialOrd + Into<f32> {
+        
+    }
+
+    pub fn cos_sim(&self, histogram: &Histogram) -> Result<f32, &'static str> {
+        let len: usize = self.count.len();
+        if histogram.count.len() != len {
+            return Err("histograms must have the same length");
+        }
+
+        let mut dot = 0.0;
+        let mut a_sq = 0.0;
+        let mut b_sq = 0.0;
+
+        let other = &histogram.count;
+
+        for idx in 0..len {
+            let b = other[idx];
+            let a = self.count[idx];
+
+            dot += a * b;
+            a_sq += a * a;
+            b_sq += b * b;
+        }
+        
+        Ok(dot / (a_sq * b_sq).sqrt())
+    }
+}

src/stdfeats/mod.rs

@@ -0,0 +1 @@
+mod historgram;