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From Graham Leggett <minf...@sharp.fm>
Subject Re: svn commit: r1026668 - /httpd/httpd/trunk/modules/proxy/mod_proxy.h
Date Sat, 23 Oct 2010 21:13:46 GMT
On 23 Oct 2010, at 10:24 PM, Jeff Trawick wrote:

>>> No; this is a dis-optimization.  You have added int-bitmath cpu  
>>> cycles
>>> to a simple int test, without gaining any storage.  Huh?
>>
>> Are you sure?
>>
>> I would expect a compiler optimiser to do the most appropriate  
>> thing, and it
>> gets us out of the habit of allocating an int or a char every time  
>> we need a
>> boolean flag.
>
> It can't reorder fields, and pointers and integers need to be on
> "natural" boundaries for performance (or even outright functionality
> on some platforms).  So there will be padding after the bit.
>
> Some Intel ABI spec would show alignment requirements for a notable
> example platform, absent of any packing pragmas.

I was referring specifically to the "int-bitmath cpu cycles". Any data  
size smaller than the bus width involves an AND at least, just to  
isolate the byte or int. It's been a while since I was doing pure  
assembly, but would be surprised if this was slower.

Regards,
Graham
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