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Old 2005-01-16, 04:04   #1
Prime95
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Default AMD64 opcode timings

Does anyone know of AMD documents that give the instruction latencies and throughput for different opcodes?

Right now, I'm mostly interested in div, idiv, mul, imul. I'm working on the trial factoring rewrite for x86-64.
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Old 2005-01-17, 00:26   #2
gdf
 
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This one ?

http://www.amd.com/us-en/assets/cont...docs/25112.PDF

Chapter C has latency tables.

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Old 2005-01-17, 14:48   #3
Prime95
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That's the one. Thanks, I missed it browsing AMD's web site.

71 clocks for division, 4 for a multiply. Looks like I need to go to great lengths to avoid divsions!
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Old 2005-01-18, 14:55   #4
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Wow. So you cannot divide and conquer this problem but instead must go forth and multiply.
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Old 2005-01-18, 16:30   #5
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If it would be so inefficient to divide, would it be more efficient to simply subtract when performing the modulo step?
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Old 2005-01-18, 21:00   #6
ewmayer
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Quote:
Originally Posted by Jeff Gilchrist
Wow. So you cannot divide and conquer this problem but instead must go forth and multiply.
...at which point the 2 snakes turned around and replied to Noah: "We can't - we're adders."

(One bad pun deserves another.)

The best solution for the extremely-long-latency divides is probably the standard Newtonian iterative inverse.
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Old 2005-01-19, 02:35   #7
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Reminds me of the ole' IBM 1620, which could divide a 66,000-digit number by a 33,000-digit number, but it would take ... hours ( on the order of 20 microseconds times number of digits in dividend times number of digits in divisor )
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Old 2005-01-19, 14:25   #8
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Quote:
Originally Posted by ewmayer
...at which point the 2 snakes turned around and replied to Noah: "We can't - we're adders."

(One bad pun deserves another.)
Noah then stomped off, muttering under his breath.

A year later, he did another census. Everything else around had multiplied manyfold, but he couldn't see the vipers anywhere. "Damn things have probably gone extinct", he muttered and went off to collect some fuel for his stove. He pulled some branches off the woodpile and was astounded to see in there dozens of tiny snakes squirming around the two adults. "How did you do it?" he exclaimed. "It was easy once we'd thought about it", the male viper replied, "we used logs."

Paul
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Old 2005-01-26, 13:22   #9
CraigB
 
Jan 2005
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Please mail me on craigb@mailme.co.za so i can put you in contact with AMD's main software optimiser. He is interested in assisting you with writing optimised code for AMD64. He is a REALLY rare resourse to have access to so please dont miss this opertunity as he has next week available to speak to you.
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Old 2005-01-26, 23:40   #10
Prime95
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I just sent you a private message
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Old 2005-01-27, 15:53   #11
CraigB
 
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Thanks & ditto :-)
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