Counting Set Bits

[dedndave]

Hutch tells me that XLAT is slow on P4's - that may only apply to 32-bit code - i dunno
you could probably make that zing with mov al,CntTable[bx] though -  :bg
i don't think we can use Michael's timing macros in 16-bit world and get meaningful readings
i could be wrong, there, but i think we need a 16-bit timer of some sort

[ilian007]

hey Veronica why you have the varible "number" it seems it doesnt do anything just printing statement is between the two number,ax  ax,number ?

[FORTRANS]

Hi Dave,

   I found some timer code from Abrash's book(s).  But
the souce was apparently OCRed somewhere along the line,
And there will be some clean-up involved.  Do you have any
interest in seeing timing results?

Regards,

Steve N.

[dedndave]

sure - although - i dunno what "OCR'ed" means - lol
but i am sure if they have workable code, we can make it fly
it would be good to have some 16-bit timing code around
it shouldn't be very large
and - all we really need is a concept
i suppose we could use the counter-timer, but that means long tests because it has poor resolution

[sinsi]

Is that the zen timer? Have a look at chapter 22 here

[dedndave]

hiyas Sinsi
i finally found the zen timer in ch 3 - lol
that looks like a good resource - thanks
let me have a look at the timer.....

[dedndave]

i found the lib with source...
http://www.programmersheaven.com/download/13855/download.aspx
at first glance, it appears to use the counter/timer chip


yah - it uses the 8253 - which means no clock cycle readings like we have come to love from Michael's macros
what would be really cool would be to learn to load and run a 16-bit app under a 32-bit console using NTVDM.EXE
then, we could use Michael's macros and subtract the load-time overhead
using the counter/timer means we need some way to measure the CPU clock frequency under 16-bit
i.e. the zen timer will yield times to the nearest 18.2 ms - not clock cycles

[sinsi]

I don't see why michael's macros can't be used in 16-bit real mode with a bit of adjustment. We can still use rdtsc, which is the guts of measuring cycles.

[dedndave]

Michael wrote a nice set of macros for us   :U

http://www.masm32.com/board/index.php?topic=12540.msg96548#msg96548

[FORTRANS]

Hi,

i dunno what "OCR'ed" means

   Sorry.  Optical Character Recognition, scan in a printed
copy, and make a guess as to what the text really is.
Error prone if the hard copy is poor.  Plus in the version I
tracked down, all the "'" got changed to something out
of M$ Word.

Is that the zen timer? Have a look at chapter 22 here

   Well, another source, but chapter 3 of that book.

Michael wrote a nice set of macros for us

   Goodie!  Saves me some effort, though it won't work
on my 80186.

Thanks.

Steve N.

[MichaelW]

i.e. the zen timer will yield times to the nearest 18.2 ms - not clock cycles

In theory it will yield times to the nearest 838ns (1 / 1193182Hz).