On Wednesday, 9 July 2014 at 10:57:33 UTC, Larry wrote:
Hello,
I extracted a part of my code written in c.
it is deliberately useless here but I would understand the
different technics to optimize such kind of code with gdc
compiler.
it currently runs under a microsecond.
Constraint : the way the code is expressed cannot be changed
much we need that double loop because there are other
operations involved in the first loop scope.
main.c :
[code]
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include "jol.h"
#include <time.h>
#include <sys/time.h>
int main(void)
{
struct timeval s,e;
gettimeofday(&s,NULL);
int pol = 5;
tes(&pol);
int arr[] = {9,16,458,2,68,5452,98,32,4,565,78,985,3215};
int len = 13-1;
int g = 0;
for (int x = 36; x >= 0 ; --x ){
// some code here erased for the test
for(int y = len ; y >= 0; --y){
//some other code here
++g;
arr[y] +=1;
}
}
gettimeofday(&e,NULL);
printf("so ? %d %lu %d %d %d",g,e.tv_usec - s.tv_usec,
arr[4],arr[9],pol);
return 0;
}
[/code]
jol.c
[code]
void tes(int * restrict a){
*a = 9;
}
[/code]
and jol.h
#ifndef JOL_H
#define JOL_H
void tes(int * restrict a);
#endif // JOL_H
Now, the D counterpart:
module main;
import std.stdio;
import std.datetime;
import jol;
int main(string[] args)
{
auto currentTime = Clock.currTime();
int pol = 5;
tes(pol);
pol = 8;
int arr[] = [9,16,458,2,68,5452,98,32,4,565,78,985,3215];
int len = 13-1;
int g = 0;
for (int x = 31; x >= 0 ; --x ){
for(int y = len ; y >= 0; --y){
++g;
arr[y] +=1;
}
}
auto currentTime2 = Clock.currTime();
writefln("Hello World %d %s %d %d\n",g, (currentTime2 -
currentTime),arr[4],arr[9]);
return 0;
}
and
module jol;
final void tes(ref int a){
a = 9;
}
Ok, the compilation options :
gdc hello.d jol.d -O3 -frelease -ftree-loop-optimize
gcc -march=native -std=c11 -O2 main.c jol.c
Now the performance :
D : 12 µs
C : < 1µs
Where does the diff comes from ? Is there a way to optimize the
d version ?
Again, I am absolutely new to D and those are my very first
line of code with it.
Thanks
Clock isn't an accurate benchmark instrument. Try
std.datetime.benchmark:
```
module main;
import std.stdio;
import std.datetime;
void tes(ref int a)
{
a = 9;
}
int[] arr = [9,16,458,2,68,5452,98,32,4,565,78,985,3215];
void foo()
{
int pol = 5;
tes(pol);
pol = 8;
int g = 0;
foreach_reverse(x; 0..31)
{
foreach_reverse(ref a; arr)
{
++g;
a += 1;
}
}
}
void main()
{
auto res = benchmark!foo(1000); // take mean of 1000 launches
writeln(res[0].msecs, " ", arr[4], " ", arr[9]);
}
```
Dmd time: 1 us
Gcc time: <= 1 us
