[fpc-devel] SSE in FPC

Vinzent Höfler JeLlyFish.software at gmx.net
Wed Dec 10 08:24:43 CET 2008

Alain Michaud wrote:
> Hi,
>   Not exactly related to this thread, but worth mentioning:
>   Some time ago I was interested in (numerical) computing some Bessel 
> function to the highest precision!
>     I looked at MMX, SSE, SSE2, SSE3, SSE4, FP87, 3D-something  etc...   
> And all that jazz...
>    It turns out that only the "old" FP87 (FPU)  has the 80 bit 
> (extended) floating format!  Anything else, and you are limited to the 
> 64 bit (double) floating numbers.
>    I fell sorry to see that even 25 years after the original 8087, 
> modern CPUs are not even capable to have the same precision!

If you need precision you have to do integer math anyway. Floating point 
numbers are always crude approximations, no matter how many bits they 
have. Considering that the numerical range of an 80-bit floating point 
number is larger than the relation between the diameter of an atom and 
the diameter of the known universe, this so-called "precision" is hardly 
ever needed. Or to express this a bit (pun intended) differently: How 
much of the universe do you expect to fit into 80 bits?


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