On Wed, 1 Dec 1999, Clive Crous wrote:
> ok, last night i went and attempted to get that semicircle algorith of mine
> working.
> i discovered 3 problems.
> 1> i need to research type casting ;-)
> 2> it'll draw a semi circle with the "curve" being 1280 degrees or
> LESS
> 3> Fixed point math doesn't work in c ??????????????
>
> I used to do a lot of graphical type programming using pascal/assembler and
> everything i did was *speed* orientated. For this reason I got quite used
> to using fixed point math in my calculations instead of relying on the FPU
> to do the grunt work.
>
> here's a quick lil snippet of my program, and the results it gave ..
> ----------------------------------------------------------------
> #define FIXED_B 16
> #define FIXED_M 1<<FIXED_B
#define FIXED_M (1<<FIXED_B)
> <snip>
> int xp,cx;
> <snip>
> cx=xp/FIXED_M;
after substitution of FIXED_M this becomes
cx=xp/1<<FIXED_B;
i.e. divide xp by 1 then left shift 16 !!!
The brackets make it
cx=xp/(1<<FIXED_B);
making the order of the operators correct.
> fprintf(stdout," %d = %d / %d\n",cx,xp,FIXED_M);
> <snip>
> ----------------------------------------------------------------
> output gives:
>
> 2808465 = 2808465 / 65536
> or
> -2808465 = 2808465 / 65536
> or
> -65536 = 2808465 / 65536
>
> ?????????? wtf ?
>
> cx always seems to be ((xp)||(-xp)||(FIXED_M)||(-FIXED_M))
> ----------------------------------------------------------------
>
> could some1 please tell me what i've done wrong ?
>
> thanks in advance
> Clive
>
>
