Re: wmemchar for unix

[monarch_dodra]

On Tuesday, 27 August 2013 at 14:43:10 UTC, H. S. Teoh wrote:
On Tue, Aug 27, 2013 at 07:37:02AM -0700, Sean Kelly wrote:
On Aug 26, 2013, at 11:57 PM, monarch_dodra 
<monarchdo...@gmail.com> wrote:

> For performance reasons, I need a "w" version of memchr.
> 
> C defines wmemchr as:
> wchar_t * wmemchr ( const wchar_t *, wchar_t, size_t );
> 
> Unfortunatly, on unix, "wchar_t" is defined a *4* bytes long,
> making wmemchr, effectivelly, "dmemchr".
> 
> Are there any "2 byte" alternatives for wmemchr on unix?

Why not cast the array to ushort[] and do a find()?  Or is 
that too
slow as well?

Optimized searches of this kind ideally translate to the 
various rep*
instructions on x86. I'm not sure if dmd does that 
optimization. If you
really feel inclined, you could do static if (X86) and throw in 
an asm
block (but that would break purity, @safety, etc., so probably 
not a
good idea).

You *might* be able to coax GDC (or LDC) to do loop unrolling 
and/or
substitution with rep* instructions with just plain D code, 
though.
Can't really say without trying it out.


T

Hum... I think that is too complicated for what I'm trying to do. 
I don't know assembly enough. Ideally, I was hoping for a 
pre-existing C function to do the work for me :)

For now, I can settle for a simple:
version (windows)
    //use fast wmemchr
else
    //use standard code

But It feels weird, in the sense that there is no reason for 
"2byte" search to be more specific to windows than for unix...