[Mplayer-dev-eng] VP3 Codec

[Arpi]

Hi,

> > >
> > > > 0x10004bd6:     mov    %cr0,%edx
> > >
> > > Oops.  So a Win32 DLL can mess with %cr0?  Amazing.
> >
> > yes. you know their slogen: win98 - everything possible
> >
> > btw that routine just checks some flags in cr0, and depending on their
> > value returns eax=0 or eax=1. i think thet can be replaced by a mov eax,0/1
> > and many nops.
> the codec seems to use much asm code, maybe it's some sort of cpu feature 
> detection.

yes:

; check to see if OS supports SIMD instructions
    mov     edx,cr0
    bt      edx,2                           ; ensure no emulation
    jnae    NoXMMSupport

    mov     edx,cr4
    bt      edx,9                           ; OS support SIMD
    jnc     NoXMMSupport

; we support XMM instructions
    mov     eax,1
    jmp     Exit

NoXMMSupport:
;    mov     eax,0                           ; OS does not support XMM instructi

so it uses cr0 to check OS support of SSE. this is why it works for Gabucino
(his k6 has no sse at all) and crashes for you.


A'rpi / Astral & ESP-team

--
mailto:arpi at thot.banki.hu
http://esp-team.scene.hu