在Go中使用GMP风格的性能处理大量数据

Question

I'm learning Go and I started using the math/big package to deal with arbitrary-length integer.

I wrote this program that computes the n-th Fibonacci number : (removed the imports) :

func main() {
    imax, _ := strconv.Atoi(os.Args[1])
    var a, b, c big.Int
    a.SetUint64(0)
    b.SetUint64(1)
    for i := 0; i < imax; i++ {
        c.Set(&b)
        b.Add(&b, &a)
        a.Set(&c)
    }
    fmt.Println(a.String())
}

Here's the code for the C program :

int main(int argc, char** argv)
{
    int imax = atoi(argv[1]);

    mpz_t a, b, c;
    mpz_inits(a, b, c, NULL);
    mpz_set_ui(a, 0);
    mpz_set_ui(b, 1);

    int i = 0;
    for (i = 0; i < imax; i++) {
        mpz_swap(a, b);
        mpz_add(b, a, b);
    }

    char* astr = NULL;
    astr = mpz_get_str(NULL, 10, a);
    printf("%s
", astr);

    return EXIT_SUCCESS;
}

The Go program computes the term 100,000 in 0.1 second (average), while the C equivalent, using the GMP lib, runs in 0.04 second only. That's two times slower.

Is there a way to get the same performance in my Go program ?

Answer 1

Don't print to stdout, it's slow. What result do you get for this code?

package main

import (
    "math/big"
    "os"
    "strconv"
)

func main() {
    max, err := strconv.Atoi(os.Args[1])
    if err != nil {
        panic(err)
    }
    a, b := big.NewInt(0), big.NewInt(1)
    for i := 0; i < max; i++ {
        a.Add(a, b)
        a, b = b, a
    }
}

Go is not hand crafted assembler code.

Your value of 100,000 is too small for a reliable benchmark. Use 1,000,000 or another value that runs for at least ten seconds.