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Subject: Re: Tables or Calculation

Author: Robert Hyatt

Date: 10:09:23 01/18/03

Go up one level in this thread


On January 18, 2003 at 05:23:54, David Rasmussen wrote:

>On January 18, 2003 at 05:19:14, Matt Taylor wrote:
>
>>On January 18, 2003 at 05:02:44, David Rasmussen wrote:
>>
>>>On January 18, 2003 at 05:00:16, Matt Taylor wrote:
>>>
>>>>
>>>>64-bit shift in something like 3 cycles when count is < 32. Pentium 4 L1 cache
>>>>latency -- 2 clocks. Athlon L1 cache latency -- 3 clocks.
>>>
>>>I don't understand this
>>
>>Yeah, broken English is a bad thing. Here's how it breaks down:
>>
>>Shift form -- 3 cycles
>>
>>Table (Athlon) -- 3 cycles
>>Table (Pentium 4) -- 2 cycles
>>
>>>>Bad performance of former indicitive of poor optimization.
>>>
>>>I don't understand this
>>
>>It means that the compiler is not doing its job. Perhaps there is an
>>optimization switch you have not enabled. Perhaps your inline function is not in
>>a header file where the C compiler can get at it. Perhaps the compiler just
>>flops on 64-bit code.
>>
>>It means basically that something is wrong. There should be almost no difference
>>in speed.
>>
>>-Matt
>
>I see. It does about the same with both Intel C++ and MSVC 7


That might be hard to check.  IE the asm stuff with intel seems to match gcc
perfectly.  Microsoft is nowhere near the same syntax, and I don't know if the
intel compiler will accept MS assembly format or not...




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