sqrt lookup

1 files changed, 25 insertions, 5 deletions

diff --git a/evc/src/pixel.rs b/evc/src/pixel.rs
index b3ef841..4fb6772 100644
--- a/evc/src/pixel.rs
+++ b/evc/src/pixel.rs
@@ -21,12 +21,32 @@ impl Ser for Pixel {
 impl Pixel {
     pub const BLACK: Pixel = Pixel { r: 0, g: 0, b: 0 };
     #[inline]
-    pub fn distance(a: Pixel, b: Pixel) -> f64 {
+    pub fn distance(a: Pixel, b: Pixel) -> usize {
         let (rd, gd, bd) = (
-            a.r.abs_diff(b.r) as f64,
-            a.r.abs_diff(b.r) as f64,
-            a.r.abs_diff(b.r) as f64,
+            a.r.abs_diff(b.r) as usize,
+            a.r.abs_diff(b.r) as usize,
+            a.r.abs_diff(b.r) as usize,
         );
-        (rd * rd + gd * gd + bd * bd).sqrt()
+        SQRT[rd + gd + bd]
     }
 }
+
+const SQRT: [usize; 256 * 3] = gen_sqrt_lookup();
+
+const fn gen_sqrt_lookup<const N: usize>() -> [usize; N] {
+    let mut arr = [0; N];
+    let mut i = 0;
+    while i < N {
+        arr[i] = sqrt(i as f32) as usize;
+        i += 1;
+    }
+    arr
+}
+
+const fn sqrt(x: f32) -> f32 {
+    let a = 1.0;
+    let a = (a + x / a) * 0.5;
+    let a = (a + x / a) * 0.5;
+    let a = (a + x / a) * 0.5;
+    a
+}