Re: First stage of Quesa changes now complete

[James W. W. <ja...@wr...>]

Roger Holmes <rog...@mi...> wrote:

>9.7% of the time in sqrt. I have switched my renderer to use std::sqrtf as
>it only ever handle floats, never doubles. Hopefully will speed things up.

Here's a quote from a recent thread on Apple's performance 
optimization mailing list:

At 4:44 PM +0000 1/23/05, Jerry wrote:
>>>  This should be faster, since it need compute fewer
>>>  bits of precision, but it is still returning the correct result,
>>>  rounded to a float.
>>
>>  On some architectures. On others the calculations will be in double
>>  precision and shortened to float on return.
>
>This is exactly what libmx does on OS X (try stepping into it in the 
>debugger), so switching to the "f" functions may actually slow you 
>down.

Moral:  Don't just hope, test.

When Shark sees often-used square root operations, it suggests that 
if you don't need full precision, you can use a special PowerPC 
instruction, frsqrte, floating reciprocal square root estimate.  I 
don't know if we want to get into platform-dependent optimizations 
though.

>I think in the release version we are checking out inputs too often, 
>for instance
>in E3Shared_Acquire we check the parameter is of type shared. We then call
>Q3Shared_GetReference which again checks its parameter is of type shared.
>It also calls E3System_Bottleneck even though we must have come into
>E3Shared_Acquire from a Q3 routine which will have already called
>E3System_Bottleneck.
>
>My question is this, can I change the call to Q3Shared_GetReference into a
>call of E3Shared::GetReference (my preferred option) or can I remove the
>check in E3Shared_Acquire  or should I leave it alone?

It's OK with me if you change the Q3Shared_GetReference to 
E3Shared::GetReference.

As long as you're messing with E3Shared_Acquire, how about combining 
the two if (theObject != NULL) statements into one?

>Can I apply you answer to all similar situations or should I ask every time?

You may apply my answer in similar situations.
-- 
   James W. Walker, ScriptPerfection Enterprises, Inc.
   <http://www.write-brain.com/>