what is Altivec? does mos suport it? and what is it good for?

He's a threadstarter....twisted threadstarter....

Seriously though, Altivec is designed for performing operations on data streams...similar PC technology is SSE/SSE2.

What do I mean by operations on data streams..decoding etc.

It's a very fast, 'small' instruction set and can operate on multiple words of data at once performing various mathematical operations that might take multiple passes on a CPU or even an FPU.

For a reference(of a very optimal example), compare the speed of say dnetc-72 regular core with an altivec enabled one.

Alternatively USE THE BLOODY GOOGLE

Steve

haha thank you

I have heard Altivec will be enabled in MOS 1.5.
The current dnetc has the Altivec code inside but is not enabled. I think i saw a screenshot of a 1 GHz G4 counting 10 Mkeys.

Quote:

Altivec is something all you Gentoo users will be obsessed with :)

Altivec can be used for really, really, really fast vector graphics (from what I was told).

Anyone for "Tepest 20,000"??


BTW: I think it's;
"WHEN THERE'S NO MORE ROOM IN HELL, THE DEAD WILL WALK the EARTH.",
but I could be wrong there too.

HEy Poundsmack

I thought I told you dont start any more threads until you OWN A PEGASOS!



magnetic Quote:

AltiVec can (amongst other things) be used to speed up applications where arithmetic or data manipulation operations on multiple data (vectors) can be carried out at the same time. It's most most frequently in applications that encode or decode video or audio data, because they tend to be very easy to divide into sequence of datablocks. Most applications can utilise AltiVec though, given that the developer(s) take this into account from the start.
Usually you can speed up operations with a factor of 2-10 times. Photoshop on OSX uses AltiVec, which is why it is so fast and can compete with the latest of Intel CPUs in benchmarks.

AltiVec existed originally only in IBMs POWER CPUs but was imported into the G4. Vector calculation in consumer-grade CPUs has existed since the middle 90s though. PA-RISC was the first "standard" CPU to support it, later Intel joined in with MMX, SSE and now SSE2. AMD call their vector unit 3DNow and Sun has something called VIS in some of their Sparc CPUs.

AltiVec is a G4's vector unit. Like other units, it runs paralelly with each other, it means, that your CPU can process (iirc) four integer mathematical instructions, one float mathematical instruction, one load/store instruction, one branch instruction, and for more four altivec instructions. This means, that the G4 can process upto 11 instructions at a single CPU cycle at ideal state, ofcourse.

The altivec itself contains four units (as above), vector permute unit, two integer and one float unit. As the AltiVec instruction works only with 128 bit data, it can operate with 4 32 bit floats through single instruction, 4 32 bit integers, 8 16 bit integers, and 16 8 bit integers. In practice it's far more complicated, that I explain here. Simply, to process, say, 16 bytes, each alone, it's enough to use a single instruction. Without altivec, You would require atleast 15 more instructions and so more CPU cycles