Date: Sun, 8 Feb 1998 07:36:33 +0000 (GMT) From: Terry Lambert <tlambert@primenet.com> To: dap@damon.com (Damon Permezel) Cc: nate@mt.sri.com, dap@damon.com, hackers@FreeBSD.ORG Subject: Re: MMX, pentium, etc Message-ID: <199802080736.AAA28517@usr02.primenet.com> In-Reply-To: <199802080537.XAA10571@damon.com> from "Damon Permezel" at Feb 7, 98 11:37:37 pm
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> > Umm, if you're using the FPU, then MMX would be a lose if you mix FPU > > and MMX instructions. Better to stick with just FPU instructions. > > Well, I'll make that decision when I know what the MMX instructions are. MMX resuses the FP registers. This is because they couldn't define new registers because new registers would not get saved and restored on process context switch for any existing OS's. Thus if you use FP, you can not use MMX, and vice versa. > All I know is, MMX are supposed to be for multimedia, and in particular enable > full-screen s/w mpeg. A lot of what I do is inverse DCT, except I go > 256x256, rather than 8x8. I will probably change to an integer iDCT > when I am able to see what the MMX instructions are: ie if they are all > integer instructions. They are. > I suppose I should change to integer anyway, but I have been spoiled by > working on machines which had decent FP performance. Most graphical applications tend to use full integer math in any case, because it tends to be faster, and you don't get rounding errors. SIDEBAR: a friend of mine used to design FPU hardware. The person he was working for -- the founder of SGI, actually -- brought him in and showed him a graphics application running [much faster than it used to]. My friend said "wow, what a neat spiral!". His boss said "it's supposed to be a circle". Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe hackers" in the body of the message
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