DOS ain't dead

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

posted by mht , Wroclaw, Poland, 25.11.2008, 22:11

> Not that I needed to know this certain behaviour of shift instructions
> yet, but knowing such details often helps.

Indeed. Knowing precisely the processor's state helps to make code simpler. In this particular case I avoid treating the cases CL = 0 and CL > 0 separately and save a conditional jump.

Complete thread:

• x86 flags after bit shifts with count = 0 - mht, 22.11.2008, 15:15
  • 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