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Re: just for fun: JSL: "q*100" hand-optimized to "(q<<6)+(q<<5)+(q<<2)"

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On 11/26/2014 2:53 AM, Andreas Leitgeb wrote:
> Last book I had mentioning those was about 8088/86 processors :-)
> And latest hearsay was, that on sufficiently new cpus even a floating
> point operations took one mere cpu-cycle - not so sure about that anymore.

Eh..... modern processors are heavily pipelined, so "taking one 
cpu-cycle" is a bit of a misnomer. The latencies of an SSE floating 
point add is 3, but it has a throughput of 1 per cycle.

Although I should point out that x86 processors have something like 
10-15 stages of "fetch" and "decode" due to the complex nature of their 
instruction set... which means the most painful thing you can do is 
mispredict a branch and have to flush the pipeline.

> I'm not very knowing about modern cpu feature names, but not-requiring
> a "superlane" sure sounds like an advantage in the lowest levels.

A modern desktop x86 processor is an out-of-order, superscalar 
processor. Effectively, this means that the "execute instruction" stage 
is basically a step where the processor ignores the order of 
instructions you listed in the assembly but rather throws them in 
several execution units as they become available. The Haswell 
microarchitecture (the latest as of this writing) has 8 execution units 
or ports: Two for loads, two for stores, one for branches, one for 
vectors, two for floating point or vectors. Basic integer operations can 
operate in any of the last four ports.

-- 
Beware of bugs in the above code; I have only proved it correct, not 
tried it. -- Donald E. Knuth

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just for fun: JSL: "q*100" hand-optimized to "(q<<6)+(q<<5)+(q<<2)" Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> - 2014-11-24 20:58 +0000
  Re: just for fun: JSL: "q*100" hand-optimized to "(q<<6)+(q<<5)+(q<<2)" Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-11-24 16:31 -0500
    Re: just for fun: JSL: "q*100" hand-optimized to "(q<<6)+(q<<5)+(q<<2)" Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> - 2014-11-26 12:39 +0000
  Re: just for fun: JSL: "q*100" hand-optimized to "(q<<6)+(q<<5)+(q<<2)" Marcel Mueller <news.5.maazl@spamgourmet.org> - 2014-11-25 23:11 +0100
    Re: just for fun: JSL: "q*100" hand-optimized to "(q<<6)+(q<<5)+(q<<2)" Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-11-25 17:45 -0500
      Re: just for fun: JSL: "q*100" hand-optimized to "(q<<6)+(q<<5)+(q<<2)" Joshua Cranmer 🐧 <Pidgeot18@verizon.invalid> - 2014-11-25 18:39 -0600
  Re: just for fun: JSL: "q*100" hand-optimized to "(q<<6)+(q<<5)+(q<<2)" Joshua Cranmer 🐧 <Pidgeot18@verizon.invalid> - 2014-11-25 18:30 -0600
    Re: just for fun: JSL: "q*100" hand-optimized to "(q<<6)+(q<<5)+(q<<2)" Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> - 2014-11-26 08:53 +0000
      Re: just for fun: JSL: "q*100" hand-optimized to "(q<<6)+(q<<5)+(q<<2)" Joshua Cranmer 🐧 <Pidgeot18@verizon.invalid> - 2014-11-26 08:10 -0600
        Re: just for fun: JSL: "q*100" hand-optimized to "(q<<6)+(q<<5)+(q<<2)" Joerg Meier <joergmmeier@arcor.de> - 2014-11-26 17:30 +0100
    Re: just for fun: JSL: "q*100" hand-optimized to "(q<<6)+(q<<5)+(q<<2)" Joerg Meier <joergmmeier@arcor.de> - 2014-11-26 17:25 +0100
      Re: just for fun: JSL: "q*100" hand-optimized to "(q<<6)+(q<<5)+(q<<2)" Joshua Cranmer 🐧 <Pidgeot18@verizon.invalid> - 2014-11-27 12:17 -0600
  Re: just for fun: JSL: "q*100" hand-optimized to "(q<<6)+(q<<5)+(q<<2)" Kevin McMurtrie <mcmurtrie@pixelmemory.us> - 2014-11-27 16:39 -0800
    Re: just for fun: JSL: "q*100" hand-optimized to "(q<<6)+(q<<5)+(q<<2)" Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> - 2014-11-29 15:17 +0000

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