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Fuel Efficiency Numbers Overstate MPG More For Cars With Small Engines

matfud Re:metric you insensitive clod! (403 comments)

Even NASA's crawler transporter gets 42 feet/gallon

about two weeks ago
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Why the Z-80's Data Pins Are Scrambled

matfud Re:gear heads (167 comments)

Damn you you opposed piston engines (which balance pretty well)

about two weeks ago
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Why the Z-80's Data Pins Are Scrambled

matfud Re:C=128 (167 comments)

Quite possibly :)

about two weeks ago
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Why the Z-80's Data Pins Are Scrambled

matfud Re:Why is it necessary to reverse engineer this? (167 comments)

When your data and or instructions are not aligned on cache boundries and/or not limited by them (4k seems pretty standard for x86 and x64 3rd level caches but the processor may have different ideas about how that is segmented for L2 and L1) then you can cause cache thrashing by trying to tune for those specific variables. (your can cause the same by not tuning for them)

You say that it is remarkable how uniform current platforms are? I am interested as to why you think that as even on just x86 and x64 there are huge differences.

Anything "exotic" excluded.
chuckugly I like to learn :)
I would like to hear why you think that. I know you can boost some tight loops by many factors if you can get then in the L1, L2, L3 cache I may learn something. For larger scale dataprocessing it can be very tricky to keep the instructions in a cache page with regularly changing data (used in small blocks) also in the cache.

And no it is not easy and never has been. It can be remarkably hard on anything other that a micro-optimisation

 

about three weeks ago
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Why the Z-80's Data Pins Are Scrambled

matfud Re:Why is it necessary to reverse engineer this? (167 comments)

I am not disagreeing with you but some of the things I pointed out above are varibles with respect to harware and most of them DO affect memory locality. If you make an assmption that x parts of data are localy cached you can be truely wrong when run on a compatable chip with a different cache layout or even the same chip but with a different offset that is only partialy aligned with the cache.

Some algorithms in general tend to keep the data used close to gether and they may benifit. Some algorihms uses data in chunks scattered all over the place but the chunks are particularly freindly for the system and they work well (keeping it cahched well).

But as I said it is remarkably hard to do those kinds of optimisation without a particular system to run on.

about three weeks ago
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Why the Z-80's Data Pins Are Scrambled

matfud Re:C=128 (167 comments)

SKIP does seem a bit limited if it is only one entry that it skips.
I think you either overran the time to execte so events had already occured or you finished early and waited for the next frame/whatever.

So how did workbench give provide windows containing HAM8 images or where they only full screen windows with a menu bar? (too long ago and I do not remember). I was using PC's back then but I was most impressed with a flatmates Amiga. Shame it struggled to run Elite :)

about three weeks ago
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Why the Z-80's Data Pins Are Scrambled

matfud Re:gear heads (167 comments)

But do you know WHY a V8 does not fire in ascending order?

about three weeks ago
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Why the Z-80's Data Pins Are Scrambled

matfud Re:5v lines (167 comments)

Many modern chips that have analog components have the analog supply and ground close to the pins used for the analog functions (for pretty obvious reasons)

You many no longer be worried about running a few extra digital datapaths to make the outside data bus be in order but you still need to seperate analog and digital functions and that limits the output pins they can use

about three weeks ago
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Why the Z-80's Data Pins Are Scrambled

matfud Re:Why is it necessary to reverse engineer this? (167 comments)

With programs generally being much much larger many such optimisations can just be lost in the noise. In some domains it is still useful but even more difficult than it was in times gone by.
Pipelining/OOE/register renaming and the multitude of processors with the same IS but remarkably different implementations, cache sizes/associativity/memory, memory size and connectivity
How many cores per CPU and how do they share those caches and memory buses.
How many independent memory banks per processor/chip (can change the cache miss time)
Memory architectre and or federated levels of connectivity (on high processor # manchines)
Operating systems can make it nigh on impossible to predict cache hits/misses as they premptively trash all your cache local code)

Just trying to optimize on modern proessors and OS's is stupidly difficult even if there were not so many variants. Still there can be significant gains sometimes (although that tends to be on small timescales relative to the OS task time. Sometime it is better to use performance libs and hope that whoever wrote them did it well :)

about three weeks ago
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Why the Z-80's Data Pins Are Scrambled

matfud Re:Why didn't they just ask Federico Faggin? (167 comments)

If you had read the article you would know that it is part of an effort to deconstruct the Z80 using optical information and yes they can see all the transistors although identifying them and thier function can be tricky as they were layed out by hand to minimise the space needed.

I have no connection to the project but reading some of the pages on the site are quite interesting if you are electronics minded.

about three weeks ago
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Why the Z-80's Data Pins Are Scrambled

matfud Re:C=128 (167 comments)

If I remember correctly changing display modes mid scan was often done so that workbench could do things like display HAM images in windows.
I think the OP may be talking about the "copper" which was a FSM with three states (MOVE, WAIT and SKIP) and a list of instructions to be processed when screen timing events occur. All three were used though and it was used for many things such as sprites and the above mentioned screen mode changes.

MOVE (put data in pretty much any register such as changing the location of a sprite to allow the sprite to be reused in another location)
WAIT (wait for a screen event such as a pixel position.)
SKIP (skip the next instruction in the copper list)
An interesting thing that could also be done in change the screen mode so that the top part of the screen displays the game and the bottom in a different mode (colour deapth/resolution) to display the game controls

Maybe I missunderstood the OP?

about three weeks ago
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Scotland Votes No To Independence

matfud Re: Civil war (474 comments)

Where is my +1 snigger vote?

It is not quite that simple as there is a fairly big movement in Argentina to reclaim the Islands.

Why? Who knows...

about a month ago
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Scotland Votes No To Independence

matfud Re:Everyone loses (474 comments)

I must agree.

It is not as simple as saying "I'm free" and I would have liked to hear more about it.

I think the most amusing was yes scotland talking about the oil and gas available. Then the shetland Isles said if our vote goes no then what oil are you talking about. It is ours. :)
   

about a month ago
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Scotland Votes No To Independence

matfud Re:BarbaraHudson: "Eat your words"... apk (474 comments)

I may not agree with you but this person has set it up to hunt you down. Oh well that is slashdot.
I am tired of the pointless posts.

about a month ago
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Scotland Votes No To Independence

matfud Re:Everyone loses (474 comments)

I thought that this was a really good point. If the isles had said fuck off to scotland then the exclusion zone would be much different. So who gets the oil?

All if and what haves but it amused me

about a month ago
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Scotland Votes No To Independence

matfud Re:Everyone loses (474 comments)

Wales says We have sheep and .... fair point.

about a month ago
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Scotland Votes No To Independence

matfud Re:Free Willy! (474 comments)

Learn why it is that way and how it mostly works.

A good idea? well probably not. It is not idealistic but also has stood the test of time (more or less)

about a month ago
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US Patent Office Seeking Consultant That Can Stamp Out Fraud By Patent Examiners

matfud Re:This is not a new or unique problem (124 comments)

Not easily as there is quite a lot of back and forth comunication over a very long period of time (up to multiple years) before a patent is granted.

about a month ago
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High School Student Builds Gun That Unlocks With Your Fingerprint

matfud Re: 999 (600 comments)

If it requires an extra digit on a display it does.

about a month ago

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