Hello, I would like to write a "popcnt" function. This works fine

ulong popcnt(ulong x)
{
asm { mov RAX, x ; popcnt RAX, RAX ; }
}

However, if I add the "naked" keyword ( which should improve performance? ) it doesn't work anymore and I can't figure out what change I am supposed to make ( aside from x[RBP] instead of x )
This function is going to be *heavily* used.

Thanks for any help.

On Saturday, 22 November 2014 at 18:30:06 UTC, Ad wrote:
> Hello, I would like to write a "popcnt" function. This works fine
>
> ulong popcnt(ulong x)
> {
> asm { mov RAX, x ; popcnt RAX, RAX ; }
> }
>
> However, if I add the "naked" keyword ( which should improve performance? ) it doesn't work anymore and I can't figure out what change I am supposed to make ( aside from x[RBP] instead of x )
> This function is going to be *heavily* used.
>
> Thanks for any help.

Last time I used naked asm simply used the calling convention to figure out the location of the parameter (e.g. RCX win64, RDI linux 64, iirc.)
N.B. on LDC & GDC there is an intrinsic for popcnt.

Am Sat, 22 Nov 2014 18:30:05 +0000
schrieb "Ad" <ad@fakmail.fg>:

> Hello, I would like to write a "popcnt" function. This works fine
> 
> ulong popcnt(ulong x)
> {
> asm { mov RAX, x ; popcnt RAX, RAX ; }
> }
> 
> However, if I add the "naked" keyword ( which should improve
> performance? ) it doesn't work anymore and I can't figure out
> what change I am supposed to make ( aside from x[RBP] instead of
> x )
> This function is going to be *heavily* used.
> 
> Thanks for any help.

It is long ago that I tried "naked", but IIRC it strips all
compiler generated code from the function and I see no 'ret'
in your function. So it probably runs into whatever code lies
behind that function in the executable.
I would use a tool like obj2asm or objdump to check what the
generated code looks like, or use a debugger that can
disassemble on the fly.

-- 
Marco