2021 day8/rust: speed up v3 to unsafe levels, remove v4

2021/day8/day8_rs/benches/unscramble.rs

@@ -1,7 +1,7 @@
 use std::{fs, path::PathBuf};
 
 use criterion::{black_box, criterion_group, criterion_main, Criterion};
-use day8_rs::{v1, v2, v3, v4};
+use day8_rs::{v1, v2, v3};
 
 pub fn criterion_benchmark(c: &mut Criterion) {
     let mut group = c.benchmark_group("unscramble");
@@ -33,13 +33,6 @@ pub fn criterion_benchmark(c: &mut Criterion) {
             }
         })
     });
-    group.bench_function("v4", |b| {
-        b.iter(|| {
-            for line in &lines {
-                let _ = unsafe { v4::unscramble(black_box(line)) };
-            }
-        })
-    });
     group.finish();
 }
 

2021/day8/day8_rs/src/lib.rs

@@ -10,4 +10,3 @@ pub struct LineResult {
 pub mod v1;
 pub mod v2;
 pub mod v3;
-pub mod v4;

2021/day8/day8_rs/src/v3.rs

@@ -50,9 +50,10 @@ pub fn unscramble(line: &str) -> LineResult {
                     break;
                 }
             }
-            Some(c) => {
+            Some(c @ b'a'..=b'g') => {
                 freq += counts[c as usize - b'a' as usize];
-            }
+            },
+            Some(_) => {}
         }
     }
 

2021/day8/day8_rs/src/v4.rs

@@ -1,63 +0,0 @@
-use crate::LineResult;
-
-const FREQ_TABLE: [usize; 256] = {
-    let mut tab = [0; 256];
-    tab[17] = 1;
-    tab[25] = 7;
-    tab[30] = 4;
-    tab[34] = 2;
-    tab[37] = 5;
-    tab[39] = 3;
-    tab[41] = 6;
-    tab[42] = 0;
-    tab[45] = 9;
-    tab[49] = 8;
-    tab
-};
-
-#[must_use]
-#[inline]
-pub unsafe fn unscramble(line: &str) -> LineResult {
-    let mut bytes = line.bytes();
-
-    let mut counts = [0; 7];
-    loop {
-        match bytes.next().unwrap() {
-            c @ b'a'..=b'g' => {
-                *unsafe { counts.get_unchecked_mut(c as usize - b'a' as usize) } += 1;
-            }
-            b'|' => break,
-            _ => {}
-        }
-    }
-
-    bytes.next();
-
-    let mut freq = 0;
-    let mut unique_digits = 0;
-    let mut number = 0;
-    loop {
-        let c = bytes.next();
-        match c {
-            Some(b' ') | None => {
-                let digit = FREQ_TABLE[freq & 0xff];
-                if [1, 4, 7, 8].contains(&digit) {
-                    unique_digits += 1;
-                }
-                number = number * 10 + digit;
-                freq = 0;
-                if c.is_none() {
-                    break;
-                }
-            }
-            Some(c) => {
-                freq += unsafe { counts.get_unchecked(c as usize - b'a' as usize) };
-            }
-        }
-    }
-
-    LineResult {
-        unique_digits,
-        number,
-    }
-}

2021/day8/day8_rs/tests/unscramble.rs

@@ -1,6 +1,6 @@
 use std::path::PathBuf;
 
-use day8_rs::{v1, v2, v3, v4, LineResult};
+use day8_rs::{v1, v2, v3, LineResult};
 
 fn test_unscramble_with_input(f: fn(&str) -> LineResult, input: &[&str]) -> LineResult {
     let mut result = LineResult {
@@ -70,12 +70,3 @@ pub fn test_unscramble_v2() {
 pub fn test_unscramble_v3() {
     test_unscramble(v3::unscramble)
 }
-
-#[test]
-pub fn test_unscramble_v4() {
-    fn safe_v4(input: &str) -> LineResult {
-        unsafe { v4::unscramble(input) }
-    }
-
-    test_unscramble(safe_v4)
-}