manual number parsing

benchmark.txt

@@ -3,4 +3,5 @@
 107 nightly, build-std
 109 native cpu (doesn't seem to work)
  95 FxHashMap
- 75 mmap, reduced UTF8 parsing (names)
+ 71 mmap, reduced UTF8 parsing (names)
+ 50 manual number parsing

src/main.rs

@@ -30,13 +30,12 @@ fn main() {
 
         let mut split = line.split(|&c| c == b';');
         let station = split.next().unwrap();
-        let parsed: f64 = String::from_utf8(split.next().unwrap().to_vec())
-            .unwrap()
-            .parse()
-            .unwrap();
+        let number = split.next().unwrap();
+        let parsed = parse_number(number);
+        // panic!();
 
         data.entry(station)
-            .and_modify(|values: &mut (f64, f64, usize, f64)| {
+            .and_modify(|values: &mut (i64, i64, usize, i64)| {
                 values.0 = values.0.min(parsed);
                 values.1 += parsed;
                 values.2 += 1;
@@ -48,7 +47,7 @@ fn main() {
     }
 
     let mut stations: Vec<_> = data.keys().collect();
-    stations.sort();
+    stations.sort_unstable();
 
     print!("{{");
 
@@ -60,9 +59,9 @@ fn main() {
 
         print!(
             "{s}={:.1}/{:.1}/{:.1}",
-            entry.0,
-            entry.1 / (entry.2 as f64),
-            entry.3
+            entry.0 as f64 / 10.,
+            (entry.1 / (entry.2 as i64)) as f64 / 10.,
+            entry.3 as f64 / 10.
         );
         if iter.peek().is_some() {
             print!(", ");
@@ -70,3 +69,37 @@ fn main() {
     }
     println!("}}");
 }
+
+fn parse_number(number: &[u8]) -> i64 {
+    let sign = if *number.first().unwrap() == b'-' {
+        -1
+    } else {
+        1
+    };
+
+    let mut iter = number.iter().rev();
+
+    // 48: ASCII '0'
+    let mut result = (iter.next().unwrap() - 48) as i64;
+    iter.next(); // skip '.'
+    result += ((iter.next().unwrap() - 48) as i64) * 10;
+
+    if let Some(hundreds) = iter.next()
+        && *hundreds != b'-'
+    {
+        result += ((hundreds - 48) as i64) * 100;
+    }
+
+    sign * result
+}
+
+#[cfg(test)]
+mod tests {
+    use super::parse_number;
+
+    #[test]
+    fn test_parse_number() {
+        let input = [49, 53, 46, 51]; // "15.3"
+        assert_eq!(parse_number(&input), 153);
+    }
+}