Use jump table

EbbDrop · Dec 22, 2024 · c8f5182 · c8f5182
1 parent 276f75b
commit c8f5182
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Showing 2 changed files with 26 additions and 29 deletions.
diff --git a/build.rs b/build.rs
@@ -225,38 +225,36 @@ fn write_day21() {
     file.write_all(&lut).unwrap();
 }
 
-// #[allow(unused)]
-// fn write_day22() {
-//     const MAX: u32 = 16777216;
+#[allow(unused)]
+fn write_day22() {
+    const MAX: u32 = 16777216;
 
-//     let mut lut = Vec::with_capacity(MAX as usize);
+    let mut lut = Vec::with_capacity(MAX as usize);
 
-//     for i in 0..MAX {
-//         let mut sn = i;
-//         for _ in 0..2000 {
-//             sn = ((sn as u64 * 64) % MAX as u64) as u32 ^ sn;
-//             sn = (sn / 32) ^ sn;
-//             sn = ((sn as u64 * 2048) % MAX as u64) as u32 ^ sn;
-//         }
+    for i in 0..MAX {
+        let mut sn = i;
+        sn = ((sn as u64 * 64) % MAX as u64) as u32 ^ sn;
+        sn = (sn / 32) ^ sn;
+        sn = ((sn as u64 * 2048) % MAX as u64) as u32 ^ sn;
 
-//         lut.push(sn);
-//     }
+        lut.push(sn);
+    }
 
-//     let lut: Box<[u32; MAX as usize]> = lut.into_boxed_slice().try_into().unwrap();
-//     let mut lut = std::mem::ManuallyDrop::new(lut);
-//     let lut: Box<[u8; 4 * MAX as usize]> = unsafe { Box::from_raw(lut.as_mut_ptr().cast()) };
+    let lut: Box<[u32; MAX as usize]> = lut.into_boxed_slice().try_into().unwrap();
+    let mut lut = std::mem::ManuallyDrop::new(lut);
+    let lut: Box<[u8; 4 * MAX as usize]> = unsafe { Box::from_raw(lut.as_mut_ptr().cast()) };
 
-//     let mut path = PathBuf::from(std::env::var("OUT_DIR").unwrap());
-//     path.push("day22.bin");
-//     let mut file = File::create(&path).unwrap();
+    let mut path = PathBuf::from(std::env::var("OUT_DIR").unwrap());
+    path.push("day22_jmp.bin");
+    let mut file = File::create(&path).unwrap();
 
-//     file.write_all(lut.as_slice()).unwrap();
-//     println!("{}", path.display());
-// }
+    file.write_all(lut.as_slice()).unwrap();
+    println!("{}", path.display());
+}
 
 fn main() {
     println!("cargo::rerun-if-changed=build.rs");
 
     write_day21();
-    // write_day22();
+    write_day22();
 }
diff --git a/src/day22.rs b/src/day22.rs
@@ -44,6 +44,9 @@ pub fn part1(s: &str) -> u64 {
     sum
 }
 
+static JMP_TBL: [u32; MAX as usize] =
+    unsafe { transmute(*include_bytes!(concat!(env!("OUT_DIR"), "/day22_jmp.bin"))) };
+
 const SEQUENCES: usize = 18 * 18 * 18 * 18;
 
 #[aoc(day22, part2)]
@@ -83,9 +86,7 @@ pub fn part2(s: &str) -> i16 {
             let mut prev = sn % 10;
 
             for _ in 0..3 {
-                sn = ((sn as u64 * 64) % MAX as u64) as u32 ^ sn;
-                sn = (sn / 32) ^ sn;
-                sn = ((sn as u64 * 2048) % MAX as u64) as u32 ^ sn;
+                sn = JMP_TBL[sn as usize];
                 let price = sn % 10;
                 let diff = price + 9 - prev;
                 diffs = diffs * 18 + diff;
@@ -94,9 +95,7 @@ pub fn part2(s: &str) -> i16 {
             }
 
             for _ in 4..2000 {
-                sn = ((sn as u64 * 64) % MAX as u64) as u32 ^ sn;
-                sn = (sn / 32) ^ sn;
-                sn = ((sn as u64 * 2048) % MAX as u64) as u32 ^ sn;
+                sn = JMP_TBL[sn as usize];
                 let price = sn % 10;
                 let diff = price + 9 - prev;
                 diffs = (diffs * 18 + diff) % SEQUENCES as u32;