Use u128 to store data

Author: EbbDrop

src/day17.rs

@@ -12,7 +12,10 @@ use aoc_runner_derive::aoc;
 // 5 5: out out b
 // 3 0: jnz a!=0 -> 0
 
-static mut RESULT: [u8; 128] = [0; 128];
+#[repr(C, align(16))]
+struct Allign([u8; 17]);
+
+static mut RESULT: Allign = Allign([0; 17]);
 
 #[aoc(day17, part1)]
 pub fn part1(s: &str) -> &'static str {
@@ -42,25 +45,31 @@ pub fn part1(s: &str) -> &'static str {
         } as u64;
 
         let result_ptr = (&raw mut RESULT).cast::<u8>();
-        let mut out_ptr = result_ptr;
-        let result_ptr = result_ptr.cast_const();
+        let out_ptr = result_ptr;
 
-        std::hint::assert_unchecked(a != 0);
-        while a != 0 {
+        let mut res = 0u128;
+        std::hint::assert_unchecked(a > 8);
+        while a > 8 {
             let b = a % 8;
             let b = b ^ x;
             let c = a >> b;
             let b = b ^ y ^ c;
 
-            out_ptr.write((b % 8) as u8 + b'0');
-            out_ptr.offset(1).write(b',');
-            out_ptr = out_ptr.offset(2);
+            res = res >> 16;
+            res |= (((b % 8) as u8 + b'0') as u128) << 112;
+            res |= (b',' as u128) << 120;
             a = a / 8;
         }
+        let b = a % 8;
+        let b = b ^ x;
+        let c = a >> b;
+        let b = b ^ y ^ c;
+        let b = (b % 8) as u8 + b'0';
 
-        let out_len = out_ptr.offset_from(result_ptr);
+        out_ptr.cast::<u128>().write(res);
+        out_ptr.offset(16).write(b);
 
-        str::from_utf8_unchecked((*&raw const RESULT).get_unchecked(..(out_len - 1) as usize))
+        std::str::from_utf8_unchecked(&(*&raw const RESULT).0)
     }
 }