DOS ain't dead

x86 flags after bit shifts with count = 0 (Developers)

posted by Rugxulo , Usono, 25.11.2008, 06:47

> I needed to know what happens to the x86 flags after executing bit shift
> instructions (SHR, SHL, etc.) when the shift count given in CL is zero.
> Unfortunately, virtually all my books and electronic documentation only
> describe the cases CL = 1 and CL > 1.

Unless you're just really really curious or trying to write an x86 emulator, I can't see much use for this. But anyways ....

> So I guess I can assume this is true for all x86 processors... Anyone with
> original 8088/8086 manuals?

Dunno, don't have the manuals. Try bugging Jim Leonard to test on his 8088. Or find someone else online who has one (Dave Dunfield, perhaps?).

However, I wouldn't trust an emulator for this (e.g. Joris' Retro) since they all have bugs.

Complete thread:

• x86 flags after bit shifts with count = 0 - mht, 22.11.2008, 15:15 (Developers)
  • x86 flags after bit shifts with count = 0 - Rugxulo, 25.11.2008, 06:47
    • x86 flags after bit shifts with count = 0 - ecm, 25.11.2008, 13:31
      • x86 flags after bit shifts with count = 0 - mht, 25.11.2008, 22:11
    • x86 flags after bit shifts with count = 0 - rr, 25.11.2008, 21:21
      • x86 flags after bit shifts with count = 0 - mht, 25.11.2008, 21:59
        • x86 flags after bit shifts with count = 0 - rr, 25.11.2008, 22:10
          • x86 flags after bit shifts with count = 0 - mht, 28.11.2008, 07:17
            • x86 flags after bit shifts with count = 0 - mht, 05.12.2008, 08:55
      • x86 flags after bit shifts with count = 0 - RayeR, 25.11.2008, 22:22
        • x86 flags after bit shifts with count = 0 - rr, 26.11.2008, 20:57
          • x86 flags after bit shifts with count = 0 - Rugxulo, 28.11.2008, 00:09
            • x86 flags after bit shifts with count = 0 - marcov, 28.11.2008, 15:41
            • x86 flags after bit shifts with count = 0 - rr, 30.11.2008, 18:33
              • x86 flags after bit shifts with count = 0 - Rugxulo, 30.11.2008, 20:53
                • portable handhelds' battery life - Rugxulo, 30.11.2008, 21:06
                • x86 flags after bit shifts with count = 0 - rr, 30.11.2008, 22:38
              • x86 flags after bit shifts with count = 0 - RayeR, 30.11.2008, 22:41