Suppose I have some memory allocated on the heap, and I have
two pointers pointing to the beginning and end of a contiguous segment
of that memory.  Is there a way I can convert those two pointers
to an array slice without actually copying anything within the segment?

Thx,
Eric

Eric:

> Suppose I have some memory allocated on the heap, and I have
> two pointers pointing to the beginning and end of a contiguous segment
> of that memory.  Is there a way I can convert those two pointers
> to an array slice without actually copying anything within the segment?

Use something like this (but make sure the length is correct):

auto mySlice = ptr1[0 .. ptr2 - ptr1];

Bye,
bearophile

On Thursday, 31 July 2014 at 19:43:00 UTC, bearophile wrote:
> Eric:
>
>> Suppose I have some memory allocated on the heap, and I have
>> two pointers pointing to the beginning and end of a contiguous segment
>> of that memory.  Is there a way I can convert those two pointers
>> to an array slice without actually copying anything within the segment?
>
> Use something like this (but make sure the length is correct):
>
> auto mySlice = ptr1[0 .. ptr2 - ptr1];
>
> Bye,
> bearophile

Thanks. That really works.  I timed doing

auto mySlice = ptr1[0 .. ptr2 - ptr1]; 1,000,000 times

versus

auto mySlice = ptr1[0 .. ptr2 - ptr1].dup; 1,000,000 times

and I am quite convinced the data is not being copied.

Eric:

> Thanks. That really works.  I timed doing
>
> auto mySlice = ptr1[0 .. ptr2 - ptr1]; 1,000,000 times
>
> versus
>
> auto mySlice = ptr1[0 .. ptr2 - ptr1].dup; 1,000,000 times
>
> and I am quite convinced the data is not being copied.

Take a look at the asm!

Bye,
bearophile

On Thursday, 31 July 2014 at 20:43:11 UTC, bearophile wrote:
>
> Take a look at the asm!
>
> Bye,
> bearophile

I use DMD and Dub, how do I view the asm?

On Thursday, 31 July 2014 at 20:59:46 UTC, Vlad Levenfeld wrote:
> On Thursday, 31 July 2014 at 20:43:11 UTC, bearophile wrote:
>>
>> Take a look at the asm!
>>
>> Bye,
>> bearophile
>
> I use DMD and Dub, how do I view the asm?

Actually I did't think to look at the asm, mainly because
I've never bothered to do it before.  But I was just reading Adam's
book the other day, and I remember seeing this:

objdump -d  -M intel simpleOctal

Not sure what the switches are for; the name of the program is simpleOctal.
But the name of the utility is objdump. (on Linux).  Not sure about Windoze.

-Eric

On Thursday, 31 July 2014 at 21:50:25 UTC, Eric wrote:
> objdump -d  -M intel simpleOctal
>
> Not sure what the switches are for;

-d
disassemble - Essential if you want to, well, disassemble.

-M intel
Intel syntax - Because no one likes AT&T syntax. Wikipedia has a
comparison:
http://en.wikipedia.org/wiki/X86_assembly_language#Syntax