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| | Unrolling AltiVec, Part 1: Introducing the PowerPC SIMD unit (Site not responding. Last check: 2007-11-03) |
 | | AltiVec does not support 64-bit values, which can be a bit of a crimp; but in AltiVec's defense, getting two operations at once might not justify the overhead of getting vectors arranged. |
 | | That said, AltiVec works best when you're doing multiple sets of operations at once, which is one of the reasons it has a large number of registers: you can load one register while another is being processed, and so on. |
 | | However, AltiVec's selection of instructions is more complete, and most of them work from two registers into a third, letting the processor perform moderately complicated vector operations entirely in registers, without touching memory until the final data is ready to come out. |
| www-128.ibm.com /developerworks/power/library/pa-unrollav1 (2797 words) |
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