lib8: implement more fastled 8 bit math as lib8 submodules

src/lib8/interpolate.rs

@@ -0,0 +1,57 @@
+use num::PrimInt;
+
+pub fn scale8(i: u8, scale: u8) -> u8 {
+    // borrowed from FastLED
+    (i as u16 * scale as u16).wrapping_shr(8) as u8
+}
+
+pub fn avg7(i: i8, j: i8) -> i8 {
+    i.unsigned_shr(1).wrapping_add(j.unsigned_shr(1)).wrapping_add(i & 0x1)
+}
+
+pub fn grad8(hash: u8, x: i8, y: i8) -> i8 {
+    let mut u: i8;
+    let mut v: i8;
+
+    if hash & 4 != 0 {
+        u = y; v = x;
+    } else {
+        u = x; v = y;
+    }
+
+    if hash & 1 != 0 {
+        u = u.wrapping_neg();
+    }
+    if hash & 2 != 0 {
+        v = v.wrapping_neg();
+    }
+
+    return avg7(u, v);
+}
+
+pub fn lerp7by8(a: i8, b: i8, frac: u8) -> i8 {
+    if b > a {
+        let delta: u8 = b.wrapping_sub(a) as u8;
+        let scaled: u8 = scale8(delta as u8, frac);
+        return a.wrapping_add(scaled as i8);
+    } else {
+        let delta: u8 = a.wrapping_sub(b) as u8;
+        let scaled: u8 = scale8(delta as u8, frac);
+        return a.wrapping_sub(scaled as i8);
+    }
+}
+
+pub fn ease8InOutQuad(i: u8) -> u8 {
+    let j = if i & 0x80 != 0 {
+        255 - i
+    } else {
+        i
+    };
+    let jj = scale8(j, j);
+    let jj2 = jj.unsigned_shl(1);
+    if i & 0x80 == 0 {
+        return jj2
+    } else {
+        return 255 - jj2;
+    }
+}