This question already has an answer here:
I have a Rust program that implements a brute-force parity check for 64-bit unsigned integers:
use std::io;
use std::io::BufRead;
fn parity(mut num: u64) -> u8 {
let mut result: u8 = 0;
while num > 0 {
result = result ^ (num & 1) as u8;
num = num >> 1;
}
result
}
fn main() {
let stdin = io::stdin();
let mut num: u64;
let mut it = stdin.lock().lines();
// skip 1st line with number of test cases
it.next();
for line in it {
num = line.unwrap().parse().unwrap();
println!("{}", parity(num));
}
}
When I feed it with input file containing 1000000 unsigned integers:
$ rustc parity.rs
$ time cat input.txt | ./parity &> /dev/null
cat input.txt 0.00s user 0.02s system 0% cpu 4.178 total
./parity &> /dev/null 3.87s user 0.32s system 99% cpu 4.195 total
And here comes a surprise - the effectively same program in Go does 4x faster:
$ go build parity.go
$ time cat input.txt | ./parity &> /dev/null
cat input.txt 0.00s user 0.03s system 3% cpu 0.952 total
./parity &> /dev/null 0.63s user 0.32s system 99% cpu 0.955 total
Here's the code in Go:
package main
import (
"bufio"
"fmt"
"os"
"strconv"
)
func parity(line string) uint64 {
var parity uint64
u, err := strconv.ParseUint(line, 10, 64)
if err != nil {
panic(err)
}
for u > 0 {
parity ^= u & 1
u >>= 1
}
return parity
}
func main() {
scanner := bufio.NewScanner(os.Stdin)
// skip line with number of cases
if !scanner.Scan() {
// panic if there's no number of test cases
panic("missing number of test cases")
}
for scanner.Scan() {
fmt.Println(parity(scanner.Text()))
}
if err := scanner.Err(); err != nil {
fmt.Fprintln(os.Stderr, "reading standard input:", err)
}
}
Versions:
$ rustc --version
rustc 1.7.0
$ go version
go version go1.6 darwin/amd64
Sample of input file, first line contains number of input values in the file:
8
7727369244898783789
2444477357490019411
4038350233697550492
8106226119927945594
1538904728446207070
0
1
18446744073709551615
Why do the Rust and Go programs I've written have such a dramatic difference in performance? I expected Rust to be a bit faster than Go in this case. Am I doing something wrong in my Rust code?
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