DOS ain't dead - INC/DEC speed

INC/DEC speed (Announce)

posted by Rugxulo , Usono, 22.12.2009, 19:01

> > INC/DEC are slow on Pentium 4 on up, and forbidden completely in 64-bit
> > mode. GCC actually generates this a lot when using -mtune=generic or
> > similar.
>
> Quotation needed. AFAIK on Pentium 4 etc. INC and DEC ar as fast as SUB 1
> ADD 1. Perhaps you want to say that multiple INCs and DECs are slower than
> ADD and SUB or that on 64-bit CPUs the carry flag is not affected by them
> as opposed to SUB 1 and ADD 1.

I don't remember exactly, so I may be saying it incorrectly. But I think it really is slower on P4s. On 64-bit, I thought the REX prefix was the INC/DEC opcode reused (so as to not pollute / bloat the opcode space).

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Complete thread:

MPLAYER update (Win32, tests needed) - DOS386, 20.12.2009, 08:28 (Announce)
- MPLAYER update (Win32, tests needed) - Rugxulo, 20.12.2009, 20:07
- MPLAYER update (Win32, tests needed) - Laaca, 21.12.2009, 01:26
  - MPLAYER update (Win32, tests needed) - ron, 21.12.2009, 03:08
    - !!! IT WORKS AGAIN !!! - DOS386, 21.12.2009, 07:55
      - !!! IT WORKS AGAIN !!! - Khusraw, 21.12.2009, 09:56
    - MPLAYER update (Win32, tests needed) - Khusraw, 21.12.2009, 09:34
      - MPLAYER update (Win32, tests needed) - Deniska, 23.12.2009, 00:23
        MPLAYER update (Win32, tests needed) - Rugxulo, 23.12.2009, 05:52
        MPLAYER update (Win32, tests needed) - Khusraw, 23.12.2009, 07:52
        MPLAYER update (Win32, tests needed) - RayeR, 25.12.2009, 01:08
        MPLAYER update (Win32, tests needed) - Khusraw, 25.12.2009, 10:48
- MPLAYER update (Win32, tests needed) - Rugxulo, 22.12.2009, 10:19
  - MPLAYER update (Win32, tests needed) - mht, 22.12.2009, 16:58
  - MPLAYER update (Win32, NOT fixed) - DOS386, 22.12.2009, 17:19
    - x86 code optimization - Rugxulo, 22.12.2009, 19:16
      - x86 code optimization - DOS386, 23.12.2009, 09:05
        x86 code optimization - marcov, 23.12.2009, 22:38
    - MPLAYER update (Win32, NOW IS fixed) - DOS386, 19.03.2010, 06:26
      - MPLAYER 31139 - DOS386, 13.05.2010, 03:49
        MPLAYER 31170 - DOS386, 06.06.2010, 15:48
  - MPLAYER update (Win32, tests needed) - Khusraw, 22.12.2009, 18:41
    - INC/DEC speed - Rugxulo, 22.12.2009, 19:01
      - INC/DEC speed - Khusraw, 24.12.2009, 13:37
        INC/DEC speed - Rugxulo, 25.12.2009, 01:00