add faster number parsing for benchmarks

2022/src/common.rs

@@ -1,7 +1,5 @@
-use std::{env, fmt::Display, str::FromStr};
-
 pub fn read_file(day: usize) -> String {
-    std::fs::read_to_string(env::var("AOC_INPUT").unwrap_or_else(|_| format!("inputs/day{:0>2}", day))).unwrap()
+    std::fs::read_to_string(std::env::var("AOC_INPUT").unwrap_or_else(|_| format!("inputs/day{:0>2}", day))).unwrap()
 }
 
 pub fn parse_nums(l: &str) -> Vec<usize> {
@@ -12,6 +10,16 @@ pub fn parse_nums_comma(l: &str) -> Vec<usize> {
     l.trim().split(',').map(parse_num).collect()
 }
 
-pub fn parse_num<T: FromStr + Display>(s: &str) -> T {
+#[cfg(debug_assertions)]
+pub fn parse_num<T: std::str::FromStr + std::fmt::Display>(s: &str) -> T {
     s.parse().unwrap_or_else(|_| panic!("Invalid number {s}"))
 }
+
+// For benchmarks.
+// This function assumes that the input will always be valid numbers and is UB otherwise
+#[cfg(not(debug_assertions))]
+pub fn parse_num<T: From<u8> + std::ops::Add<T, Output = T> + std::ops::Mul<T, Output = T>>(s: &str) -> T {
+    let mut digits = s.bytes().map(|b| T::from(b - b'0'));
+    let start = unsafe { digits.next().unwrap_unchecked() };
+    digits.fold(start, |acc, n| acc * T::from(10) + n)
+}