Re: fixed point vs floating point

[John.A.Limpert.1@gsfc.nasa.gov (John A. Limpert)]

tmoran@bix.com (Tom Moran) wrote:

>But "type degrees is delta 1.0/16 range 0.0 .. 360.0;" has only 5760
>possible values, and a table lookup with a table of 5760 entries is
>often quite reasonable, and surely faster than converting to fp,
>calculating a sin, and converting back.  Not to mention if the
>function is not just sin, but, say the 6th power of the cos (in a
>Phong illumination calculation, say).

Table lookup has been an important speed optimization for many years,
but does it still work well on newer processors? My experience is that
I don't get the speed improvements that I expect, probably due to the
increasing penalty for cache misses on faster processors. The trend
seems to be that branch-free pipelined code will run faster than table
lookups. Have optimizing compilers kept up with the shifting
tradeoffs?