From: Lars-Erik Bjørk
Date: November 22 2008 3:56pm
Subject: Re: Request for review bug#40614
List-Archive: http://lists.mysql.com/falcon/203
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Vlad,

Thanks for the comments, you do have a valid point there. There is no  
need to take the extra step of computing the intermediate result.  
Especially when it may lead to ambiguous results. I will change my  
implementation accordingly :)

Btw, that was a fast review on a Saturday!

/Lars-Erik


On Nov 22, 2008, at 4:24 PM, Vladislav Vaintroub wrote:

> Lars-Erik, I like the comments and test-case very impressive. Very  
> good:)
>
> There is one subtlety though. Unlike in math, relying on difference  
> between
> values when making comparisons does not always work, specifically in  
> corner
> cases, where difference would overflow the range for the data type.
>
> Illustration is the program below. It will incorrectly think that
> INT_MAX(==2147483647) < INT_MIN(-2147483648) and assert ,because  
> INT_MAX -
> INT_MIN is -1.
>
> #include <limits.h>
> #include <assert.h>
>
> int compare(int a, int b)
> {
> 	return (a-b);
> }
>
> int main(int argc, char argv[])
> {
> 	int result = compare(INT_MAX,INT_MIN);
> 	assert(result > 0);
> 	return 0;
> }
>
> I propose move away from computing difference and consistently do  
> something
> like
>
> if (a < b)
>   return -1;
> if (a > b)
>   return 1;
> return 0;
>
> for all datatypes instead.
>
>
>
>
>> -----Original Message-----
>> From: Lars-Erik.Bjork@stripped [mailto:Lars-Erik.Bjork@stripped]
>> Sent: Saturday, November 22, 2008 1:35 PM
>> To: falcon@stripped
>> Subject: Request for review bug#40614
>>
>> Hi all,
>>
>> The patch is described in the commit, available at
>> http://lists.mysql.com/commits/59617
>>
>> Have a nice weekend!
>>
>> --
>> Falcon Storage Engine Mailing List
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>> To unsubscribe:    http://lists.mysql.com/falcon?unsub=wlad@stripped
>
>
>
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