some improvements by reducing the casts, implemented a get_pos function to get position of byte in byteslice by bitmasking... slightly slower

src/main/rust/src/bin/single_thread.rs

@@ -4,7 +4,8 @@ use std::collections::HashMap;
 use std::fs::File;
 use std::io::{BufRead, BufReader};
 use std::time::Instant;
-use onebrc::{hashstr, StationMeasurements};
+
+use onebrc::{hashstr, parse_temp, StationMeasurements};
 
 const DEFAULT_HASHMAP_LENGTH: usize = 10000;
 
@@ -24,7 +25,7 @@ fn main() {
         let (station, temp) = line.rsplit_once(|&byte| byte == b';').unwrap();
         let hash = hashstr(station);
         let station = unsafe { String::from_utf8_unchecked(Vec::from(station)) };
-        let temp = onebrc::parse_temp(temp.split_last().unwrap().1);
+        let temp = parse_temp(temp.split_last().unwrap().1);
         let measurements_option = stations.get_mut(&hash);
         if let Some((_, measurements)) = measurements_option {
             measurements.update(temp);

src/main/rust/src/lib.rs

@@ -47,9 +47,9 @@ pub fn format_nums(num: usize) -> String {
 }
 
 #[inline]
-pub const fn get_digit(b: u8) -> u32 {
+pub const fn get_digit(b: u8) -> isize {
     // wrapping_sub('0' as u32) same as - 48 but less magical
-    (b as u32).wrapping_sub('0' as u32)
+    (b as isize).wrapping_sub('0' as isize)
 }
 
 #[inline]
@@ -63,9 +63,9 @@ pub fn parse_temp(bytes: &[u8]) -> isize {
         _x => panic!("could not parse temp: is_negative = {is_negative}, length = {}", bytes.len()),
     };
     if is_negative {
-        -(as_decimal as isize)
+        -as_decimal
     } else {
-        as_decimal as isize
+        as_decimal
     }
 }
 
@@ -123,32 +123,85 @@ pub fn new_parse_temp(bytes: &[u8]) -> isize {
 // }
 
 #[inline]
-pub fn parse_line(line: &[u8]) -> (&[u8], &[u8]) {
-    let mut idx = 0;
-    let line_len = line.len();
-    while idx < line_len && line[idx] != b';' {
-        idx += 1;
+pub fn get_pos(bytes: &[u8], find: u8) -> Option<u32> {
+    let chunks = bytes.windows(4);
+    let mut pos = 0;
+    for chunk in chunks {
+        let inner_pos = get_pos_in_chunk(chunk, find);
+        if inner_pos < chunk.len() as u32 {
+            return Some(pos + inner_pos);
+        }
+        pos += 1;
     }
-    let station = &line[0..idx];
-    (station, &line[(idx+1)..(line_len-1)])
+    None
+}
+
+#[inline]
+fn get_pos_in_chunk(byte_chunk: &[u8], find: u8) -> u32 {
+    let find_hex = u32::from_be_bytes([find; 4]);
+    let x = u32::from_be_bytes(byte_chunk.try_into().unwrap()) ^ find_hex;
+    let mask = (x - 0x01010101) & (!x & (0x80808080));
+    u32::leading_zeros(mask) >> 3
 }
 
 #[cfg(test)]
 mod tests {
-    use crate::new_parse_temp;
+    use crate::{get_pos, hashstr, new_parse_temp};
 
     #[test]
-    fn test_new_parse_temp() {
+    fn test_new_parse_temp_max() {
         let temp_max = new_parse_temp("99.9".as_bytes());
-        let temp_min = new_parse_temp("-99.9".as_bytes());
-        let temp_0 = new_parse_temp("0.0".as_bytes());
-        let temp_10 = new_parse_temp("10.0".as_bytes());
-        let temp_neg_10 = new_parse_temp("-10.0".as_bytes());
-
         assert_eq!(temp_max, 999);
+    }
+
+    #[test]
+    fn test_new_parse_temp_min() {
+        let temp_min = new_parse_temp("-99.9".as_bytes());
         assert_eq!(temp_min, -999);
+    }
+
+    #[test]
+    fn test_new_parse_temp_zero() {
+        let temp_0 = new_parse_temp("0.0".as_bytes());
         assert_eq!(temp_0, 0);
-        assert_eq!(temp_10, 100);
-        assert_eq!(temp_neg_10, -100);
+    }
+
+    #[test]
+    fn test_new_parse_temp_pos() {
+        let temp_10 = new_parse_temp("9.9".as_bytes());
+        assert_eq!(temp_10, 99);
+    }
+
+    #[test]
+    fn test_new_parse_temp_neg() {
+        let temp_neg_10 = new_parse_temp("-9.9".as_bytes());
+        assert_eq!(temp_neg_10, -99);
+    }
+
+    #[test]
+    fn test_hashstr() {
+        let hash_1 = hashstr(b"abcdefghijk");
+        let hash_2 = hashstr(b"kjihgfedcba");
+        let hash_3 = hashstr(b"abba");
+        let hash_4 = hashstr(b"baab");
+
+        assert_ne!(hash_1, hash_2);
+        assert_ne!(hash_3, hash_4);
+    }
+
+    #[test]
+    fn test_getpos() {
+        let semi_bytes = vec![0_u8, 0_u8, 0_u8, 0_u8, 0_u8, 0_u8, 0_u8, 0_u8, b';', 0_u8, 0_u8];
+        let semi_bytes = semi_bytes.as_slice();
+        let pos = get_pos(semi_bytes, b';').unwrap();
+        assert_eq!(pos, 8);
+    }
+
+    #[test]
+    fn test_getpos_empty() {
+        let semi_bytes = vec![0_u8, 0_u8, 0_u8, 0_u8, 0_u8, 0_u8, 0_u8, 0_u8, 0_u8, 0_u8];
+        let semi_bytes = semi_bytes.as_slice();
+        let pos = get_pos(semi_bytes, b';');
+        assert_eq!(pos, None);
     }
 }