[gameprogrammer] Re: Fixed point math

Hi,

Yes I can get by with 14.16 format. As long as the higher bit is 16 I should 
be able to get along with it. How exactly would I implement 1.15 ? Could you 
give me an example of converting a number to 1.15. However I am not sure  if 
I can get by with 1.15.

Thanks.
Gautam


>On Wed, 2004-10-20 at 12:08, Gautam Narain wrote:
>Hi,
>
>>Kevin, you are partly right and partly wrong. I am targetting Opengl ES 
>>which needs fixed point support. However I am targetting the Khronos 
>>contest and not the gamedev one and a linux application(game). Anyway I do 
>>this for a hobby so I figured well - I will aim for the contest.
>>
>>I changed the following in the code
>>long long e = FIXMUL(c, d);

>My guess is that it is doing a 32 bit multiply and then converting the
>result to 64 bits. It would do that because c and d are 32 bit numbers.

>>
>>This gives me zero as well. However when I do it with floating point 
>>numbers, I get the values after the decimal(fraction) correctly but the 
>>main number is zero. Any ideas why it could be truncating ? Lastly I don't 
>>think OpenGL ES has 64 bit support(so long long may not be supported). So 
>>I will probably be stuck with int's. But I need to use 15.16 fixed point 
>>variables. Should I do everything in 7.8 bit and the convert to 15.16 bit 
>>? Would this slow things down or make it equal to if I did it with just 
>>floats ?

>Why must you use 15.16 numbers? BTW, if you multiply a 7.8 number by
>another 7.8 number you get a 14.16 number. Can you get by with
>converting everything to a fraction and using something like 1.15
>numbers?

 >               Bob Pendleton

>
>>Thanks
>>
>>Gautam

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