dongliuliu0385
2016-03-20 23:14
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为什么在执行相同的按位和I / O操作时,我的Rust程序比Go程序慢4倍? [重复]

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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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