Re: Functional vs simple code

[Timon Gehr]

On 10/02/2012 10:48 PM, ixid wrote:

Without optimization the range and algorithm method takes about 10 times
as long as the simple code below it, with no array bounds checking and
optimization it takes six times as long. Why is the difference so huge?
I'd expect a moderate overhead but that's a big difference.

module main;
import std.stdio, std.algorithm, std.range, std.datetime;

enum MAX = 10_000_000UL;

void main() {
     StopWatch sw;
     sw.start;

     auto sum1 = MAX.iota.map!(x => x * x).reduce!"a + b";

     sw.peek.msecs.writeln("msecs");
     sum1.writeln;
     sw.start;

     ulong sum2 = 0;
     foreach(i;0..MAX)
         sum2 += i * i;

     sw.peek.msecs.writeln("msecs");

     sum2.writeln;
}

$ cat ixidbench.d
module main;
import std.stdio, std.algorithm, std.range, std.datetime;

enum MAX = 10_000_000_000UL;

void main() {
        StopWatch sw;
        sw.start;

        auto sum1 = MAX.iota.map!(x => x * x).reduce!"a + b";

        sw.stop;
        sw.peek.msecs.writeln("msecs");
        sum1.writeln;
        sw.reset;
        sw.start;

        ulong sum2 = 0;
        foreach(i;0..MAX)
                sum2 += i * i;

        sw.stop;
        sw.peek.msecs.writeln("msecs");

        sum2.writeln;
}
$ ldmd2 -O -release -inline ixidbench.d -ofixidbench
$ ./ixidbench
6528msecs
7032546979563742720
7518msecs
7032546979563742720