Re: math.log() benchmark of first 1 billion int using std.parallelism

[Daniel Kozak via Digitalmars-d-learn]

On Tuesday, 23 December 2014 at 10:39:13 UTC, Iov Gherman wrote:

These multi-threaded benchmarks can be very sensitive to their 
environment, you should try running it with nice -20 and do 
multiple passes to get a vague idea of the variability in the 
result. Also, it's important to minimise the number of other 
running processes.

I did not use the nice parameter but I always ran them multiple 
times and choose the average time. My system has very few 
running processes, minimalist ArchLinux with Xfce4 so I don't 
think the running processes are affecting in any way my tests.

And what about single threaded version?

Btw. One reason why DMD is faster is because it use fyl2x X87 
instruction

here is version for others compilers:

import std.math, std.stdio, std.datetime;

enum SIZE = 100_000_000;

version(GNU)
{
        real mylog(double x) pure nothrow
        {
                real result;
                double y = LN2;
                asm
                {
                        "fldl   %2\n"
                        "fldl   %1\n"
                        "fyl2x"
                        : "=t" (result) : "m" (x), "m" (y);
                }
                return result;
        }
}
else
{
        real mylog(double x) pure nothrow
        {
                return yl2x(x, LN2);
        }
}

void main() {
        
        auto t1 = Clock.currTime();
        auto logs = new double[SIZE];
        
        foreach (i; 0 .. SIZE)
        {
                logs[i] = mylog(i + 1.0);
        }

        auto t2 = Clock.currTime();

        writeln("time: ", (t2 - t1));
}

But it is faster only on all Intel CPU, but on one of my AMD it 
is slower than core.stdc.log