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