• Ad (11/11) Nov 22 2014 Hello, I would like to write a "popcnt" function. This works fine
• safety0ff (5/17) Nov 22 2014 Last time I used naked asm simply used the calling convention to
• Marco Leise (11/25) Nov 22 2014 It is long ago that I tried "naked", but IIRC it strips all

"Ad" <ad fakmail.fg> writes:

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.

"safety0ff" <safety0ff.dev gmail.com> writes:

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.

Marco Leise <Marco.Leise gmx.de> writes:

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