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Subject: Re: a question about speed

Author: Walter Faxon

Date: 12:55:25 01/05/03

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On January 04, 2003 at 23:32:43, Robert Hyatt wrote:

>On January 04, 2003 at 15:32:40, Walter Faxon wrote:
>
>>On January 03, 2003 at 19:52:06, Matt Taylor wrote:

<snip>

>>>The compiler -should- recognize that 2 * to = to << 1
>>
>>ONLY IF 'to' is guaranteed positive.  Try:  "2 * (unsigned)to".  Or explicit
>>shifting is always ok in my book.  Use a comment or #if'ed-out debug code if you
>>want to keep things clear.
>>
>
>I'm missing something...
>
>-1<<1 is the same thing as -1*2...  whether it is positive or negative does
>not matter at all.

<snip>

Sorry.  Leftshift always ok for integer multiply by power of 2.  It's rightshift
for divide by power of 2 that requires an unsigned operand.  Mea culpa.

-- Walter



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