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digitalmars.D.learn - Is there any overhead iterating over a pointer using a slice?

reply Gary Willoughby <dev nomad.so> writes:
In relation to this thread:

http://forum.dlang.org/thread/ddckhvcxlyuvuiyazpqy forum.dlang.org

Where I asked about slicing a pointer, I have another question:

If I have a pointer and iterate over it using a slice, like this:

	T* foo = &data;

	foreach (element; foo[0 .. length])
	{
		...
	}

Is there any overhead compared with pointer arithmetic in a for 
loop?
May 31 2016
next sibling parent Adam D. Ruppe <destructionator gmail.com> writes:
On Tuesday, 31 May 2016 at 18:55:18 UTC, Gary Willoughby wrote:

 Is there any overhead compared with pointer arithmetic in a for 
 loop?


Very very little. The slice will ensure start and stop indexes 
are in bounds before the loop (and throw an RangeError if it 
isn't), but inside the loop, it should generate exactly the same 
code.
May 31 2016
prev sibling parent reply Johan Engelen <j j.nl> writes:
On Tuesday, 31 May 2016 at 18:55:18 UTC, Gary Willoughby wrote:

 If I have a pointer and iterate over it using a slice, like 
 this:

 	T* foo = &data;

 	foreach (element; foo[0 .. length])
 	{
 		...
 	}

 Is there any overhead compared with pointer arithmetic in a for 
 loop?


Use the assembly output of your compiler to check! :-)  It's fun 
to look at.
For example, with GDC:
http://goo.gl/Ur9Srv

No difference.

cheers,
   Johan
May 31 2016
parent Gary Willoughby <dev nomad.so> writes:
On Tuesday, 31 May 2016 at 20:52:20 UTC, Johan Engelen wrote:

 On Tuesday, 31 May 2016 at 18:55:18 UTC, Gary Willoughby wrote:

 If I have a pointer and iterate over it using a slice, like 
 this:

 	T* foo = &data;

 	foreach (element; foo[0 .. length])
 	{
 		...
 	}

 Is there any overhead compared with pointer arithmetic in a 
 for loop?


 Use the assembly output of your compiler to check! :-)  It's 
 fun to look at.
 For example, with GDC:
 http://goo.gl/Ur9Srv

 No difference.

 cheers,
   Johan


That's pretty nice.
Jun 01 2016