Set / Clear Flags

JonnyMac

A long time ago there was a thread about setting and clearing the C and Z flags -- can't seem to find it. The thread may have been started by Phil, but I think it was in the old forums because a bookmark I have is broken.

Does anyone have a link or cool PASM tips for setting and clearing the C and Z flags? My immediate need is to clear the C flag; this is what I'm thinking:

xor     $, $                    nr, wc  ' clear c flag

Phil Pilgrim (PhiPi)

Here's the thread:

http://forums.parallax.com/showthread.php/108002

-Phil

JonnyMac

Thanks, Phil!

lonesock

Using the instructions themselves as data always struck me as very clever, but since I have a hard time parsing what the code is supposed to do I tend to use an automatically-zeroed special register, like (untested...from memory):

{ C=0 Z=0 } cmpsub outb, #1 wc,wz
  { C=1 Z=1 } cmpsub outb, #0 wc,wz
  { C=0 Z=1 } cmp  outb, #0 wc,wz
  { C=1 Z=0 } cmp  outb, #1 wc,wz

Jonathan

HydraHacker

Hi Guys,
I believe that this code below will save both the Z & C flags and restore them.

save flags

muxnz ZC, #2
muxc ZC, #1

restore

sar ZC, #1 wz, wc

HydraHacker

Phil Pilgrim (PhiPi)

HydraHacker wrote:

save flags

muxnz ZC, #2
muxc ZC, #1

restore

sar ZC, #1

Very slick, indeed (but don't forget to wc,wz in the sar).

HydraHacker

Thanks Phil,

I added the WZ and WC effects, I had it wrote down on my paper but forgot to include it.

HydraHacker