On 09/19/2011 04:08 PM, Andrei Alexandrescu wrote:
On 9/19/11 6:25 AM, Steven Schveighoffer wrote:
On Sun, 18 Sep 2011 15:34:16 -0400, Timon Gehr <timon.g...@gmx.ch> wrote:
On 09/18/2011 08:28 PM, Andrei Alexandrescu wrote:
That would allow us to e.g. switch from the
pointer+length representation to the arguably better pointer+pointer
representation with ease.
In what way is that representation better?
I agree, I don't see why the representation is inherently better. Some
operations become higher performance (i.e. popFront), and some become
worse (i.e. length). Most of the others are a wash.
That's where frequency of use comes into play. I'm thinking popFront
would be used most often, and it touches two words.
Andrei
Normally, each popFront comes with an accompanying empty, and the
comparison against 0 is faster after a decrement than the comparison of
two arbitrary pointer values.
Now a benchmark:
import std.datetime, std.stdio;
int[100000] a;
void f1(){
for(auto ptr=a.ptr, len=a.length+1; len; ++ptr, --len){}
}
void f2(){
for(auto b=a.ptr, e=a.ptr+a.length; b!=e; b++){}
}
void main(){
auto b=benchmark!(f1,f2)(100000);
writeln(b[0].to!("seconds",double)," ", b[1].to!("seconds",double));
}
On my machine: (-O -release -inline)
4.00256 4.00099
The difference is inconceivable on my oldish Core 2 Duo processor. Yet
there is a reproducible difference that indicates that you were right
about the pointer-pointer representation being slightly faster for that
use case.
