Small lut?

Author: EbbDrop

src/day8.rs

@@ -20,30 +20,20 @@ pub fn part1(s: &str) -> u32 {
     unsafe { part1_inner(s) }
 }
 
-// const SHIFT_LUT: [u64; (SIZE * SIZE * 2) as usize] = {
-//     let mut lut = [0; (SIZE * SIZE * 2) as usize];
+const SHIFT_LUT: [u64; (SIZE * 3) as usize] = {
+    let mut lut = [0; (SIZE * 3) as usize];
 
-//     let mut x = 0;
-//     while x < SIZE {
-//         let mut diff_x = -SIZE + 1;
-
-//         let field = 1 << x;
-
-//         while diff_x < SIZE {
-//             lut[(x * SIZE * 2 + diff_x + SIZE - 1) as usize] = if diff_x.is_positive() {
-//                 field << diff_x
-//             } else {
-//                 field >> -diff_x
-//             };
-
-//             diff_x += 1;
-//         }
+    let mut i = 0;
+    while i < SIZE * 2 {
+        if i >= SIZE - 1 {
+            lut[i as usize] = 1 << i - SIZE + 1;
+        }
 
-//         x += 1;
-//     }
+        i += 1;
+    }
 
-//     lut
-// };
+    lut
+};
 
 unsafe fn part1_inner(s: &str) -> u32 {
     #[cfg(not(test))]
@@ -79,21 +69,15 @@ unsafe fn part1_inner(s: &str) -> u32 {
             if *mast_y >= diff_y {
                 let node_y = mast_y - diff_y;
 
-                *antinodes.get_unchecked_mut(node_y as usize) |= if diff_x.is_positive() {
-                    1 << mast_x << diff_x
-                } else {
-                    1 << mast_x >> -diff_x
-                };
+                *antinodes.get_unchecked_mut(node_y as usize) |=
+                    SHIFT_LUT[(mast_x + diff_x + SIZE - 1) as usize];
             }
 
             if new_y + diff_y < SIZE {
                 let node_y = new_y + diff_y;
 
-                *antinodes.get_unchecked_mut(node_y as usize) |= if diff_x.is_positive() {
-                    1 << new_x << diff_x
-                } else {
-                    1 << new_x >> -diff_x
-                };
+                *antinodes.get_unchecked_mut(node_y as usize) |=
+                    SHIFT_LUT[(new_x - diff_x + SIZE - 1) as usize];
             }
         }