ingo <ing### [at] homenl> wrote:
: 100000 x #declare I=I+1; in a script versus a loop:

:        kernel user   total
: loop  : 2.98  10.20  13.19
: script: 0.90   4.19   5.09 sec.

  Loop-unrolling is indeed one of the oldest optimization tricks. The basic
idea is that if you unroll the loop, the interpreter doesn't have to parse
the #while and #end in each loop, but it just has to interpret the commands
inside the loop n times.
  The speedup seen above is most probably caused by the fact that POV-Ray
doesn't need to read and interpret the "#while" and "end" strings anymore to
do the same thing. Also not having to seek the file might speed up a bit, but
I don't think that's the main bottleneck here.

  (Note that when we are optimizing assembly code for a current processor,
loop-unrolling may not be a good optimization anymore; it may even be that
it slows down the program. Nowadays processors have extremely advanced
loop optimizations in themselves and usually we don't need to "guide" the
processor in doing it. On the other hand, loop unrolling means more code,
which means that the code cache will fill up faster, which means slower code.
Of course this is not the case in POV-Ray, which is, may I say, an extremely
primitive interpreter.)

-- 
#macro N(D,I)#if(I<6)cylinder{M()#local D[I]=div(D[I],104);M().5,2pigment{
rgb M()}}N(D,(D[I]>99?I:I+1))#end#end#macro M()<mod(D[I],13)-6,mod(div(D[I
],13),8)-3,10>#end blob{N(array[6]{11117333955,
7382340,3358,3900569407,970,4254934330},0)}//                     - Warp -

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