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Subject: Re: question about branchless code

Author: Uri Blass

Date: 04:44:19 02/27/03

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On February 27, 2003 at 05:23:25, Tony Werten wrote:

>On February 26, 2003 at 14:04:16, Uri Blass wrote:
>
>>I had the following code in my program
>>
>>do
>>{
>>...
>>if (info[target]==EMPTA)
>>  target+=8;
>>else
>>  target=64;
>>}
>>while (target<64)
>
>Less branches:
>
>do
>{
>...
>  tmp:=(info[target]!=EMPTY);  // maybe typecast to int ?
>  target+=(tmp*256)+8;
>} while (target<64);
>
>if (target>256) target=64;
>
>
>But I'm not sure if this works in C. (In pascal compares are garantied to return
>0 or 1 )

It works in C(except the fact that I need to use a varaible for tmp)

I even do not need the last if (target>256) target==64 because target is not
used after the loop but I am not sure if it makes me faster.

I have many similiar loops and by comparing times by changing one loop
I find that it is even slightly slower.

I used a global varaible for tmp because if I use a local caraible that I need
to define at the beginning of the function then it means that I need to change
all the similiar functions in order to practically use it.

Uri



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