Actually I get the same as the original program on my mac.
time ./ccode
sum=606329794183272.375000
./ccode 0.17s user 0.00s system 98% cpu 0.170 total
The Go version -O2 -Wall
time ./pow
sum=6.063297941832724e+14./pow 5.47s user 0.01s system 99% cpu 5.490 total
fre 4 aug. 2017 kl 09:38 skrev Sebastien Binet <bi...@cern.ch>:
> Dorival,
>
> On Fri, Aug 4, 2017 at 8:20 AM, Dorival Pedroso <dorival.pedr...@gmail.com
> > wrote:
>
>> I've noticed that this C code:
>>
>> #include "math.h"
>> int main() {
>> double x = 2.5;
>> int Nmax = 10000000;
>> for (int N=0; N<Nmax; N++) {
>> for (int i=0; i<20; i++) {
>> pow(x, i);
>> }
>> }
>> }
>>
>> can run up to 50x faster than this Go code:
>>
>> package main
>>
>> import "math"
>>
>> func main() {
>> x := 2.5
>> Nmax := 10000000
>> for N := 0; N < Nmax; N++ {
>> for i := 0; i < 20; i++ {
>> math.Pow(x, float64(i))
>> }
>> }
>> }
>>
>> The C code was compiled with: gcc -O2 ccode.c -o ccode -lm
>> then run with time ./ccode
>>
>> The Go code was compiled with: go build gcode.go
>> then run with time ./gcode
>>
>> I've used the time command on Linux (Ubuntu) to get some estimate.
>>
>> So the question is: how can we make the Go code faster?
>>
> no, the question is whether you are really doing what you think you are
> doing in C.
> that's the usual question with benchmarking.
>
> with your initial C code, I get this on my machine:
>
> $> time ./c-code
> real 0m0.261s
> user 0m0.260s
> sys 0m0.000s
>
> and this for the Go code:
>
> $> time ./go-code
> real 0m12.781s
> user 0m12.784s
> sys 0m0.000s
>
> then, modifying the C code to make sure the compiler won't elide the pow
> computation altogether:
>
> #include <math.h>
> #include <stdio.h>
>
> int main() {
> double sum = 0;
> double x = 2.5;
> int Nmax = 10000000;
> for (int N=0; N<Nmax; N++) {
> for (int i=0; i<20; i++) {
> sum += pow(x, i);
> }
> }
> printf("sum=%f\n", sum);
> }
>
> I now get:
>
> $> time ./c-code-sum
> sum=606329794183272.375000
>
> real 0m18.385s
> user 0m18.377s
> sys 0m0.000s
>
> applying the same modifications to the Go code:
>
> $> time ./go-code-sum
>
> sum=6.063297941832724e+14
>
> real 0m12.685s
> user 0m12.673s
> sys 0m0.010s
>
> -s
>
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