Performance

[bearophile via Digitalmars-d]

On Friday, 30 May 2014 at 13:35:59 UTC, Thomas wrote:
> I made the following performance test, which adds 10^9 Double’s 
> on Linux with the latest dmd compiler in the Eclipse IDE and 
> with the Gdc-Compiler also on Linux. Then the same test was 
> done with C++ on Linux and with Scala in the Java ecosystem on 
> Linux. All the testing was done on the same PC.
> The results for one addition are:
>
> D-DMD: 3.1 nanoseconds
> D-GDC: 3.8 nanoseconds
> C++: 1.0 nanoseconds
> Scala: 1.0 nanoseconds

Your code written in a more idiomatic way (I have commented out 
new language features):


import std.stdio, std.datetime;

double plus(in uint nSteps) pure nothrow @safe /*@nogc*/ {
     enum double p0 = 0.0045;
     enum double p1 = 1.00045452-p0;

     double tot = 1.346346;
     auto b = true;

     foreach (immutable i; 0 .. nSteps) {
         final switch (b) {
             case true:
                 tot += p0;
                 break;
             case false:
                 tot += p1;
                 break;
         }

         b = !b;
     }

     return tot;
}

void run(alias func, string funcName)(in uint nSteps) {
     StopWatch sw;
     sw.start;
     immutable result = func(nSteps);
     sw.stop;
     writeln(funcName);
     writefln("Last: %f", result);
     //writeln("Time per op: ", sw.peek.nsecs / real(nSteps));
     writeln("Time per op: ", sw.peek.nsecs / cast(real)nSteps);
}

void main() {
     run!(plus, "plus")(1_000_000_000U);
}

(But there is also a benchmark helper around).

ldmd2 -O -release -inline -noboundscheck test.d

Using LDC2 compiler, on my system the output is:

plus
Last: 500227252.496398
Time per op: 9.41424

Bye,
bearophile