Why Intel decimal library?

[Claudio L.]

(03-11-2014 10:33 PM)Paul Dale Wrote:  As Marcus wrote, the 34S uses a modified decNumber library for its basic arithmetic. Internally I work with higher than decimal128 precision and convert before and after operations. In this case, of not using decmial64 or decimal128 for much bar storage) even those old comparisons indicate that the Intel library would be faster.

decNumber is very slow when you use the actual decNumber format. Using the decDouble (decimal64) or decQuad (decimal128) seems to be faster than the Intel one, at least in those numbers.

(03-11-2014 10:33 PM)Paul Dale Wrote:  The comparison is somewhat misleading in that there isn't mention of the many functions included in the Intel library but not in decNumber (but not vice versa).

Very misleading, I was lead to believe that the Intel library didn't have trascendental functions. I see now why it would be a better choice.

(03-11-2014 10:33 PM)Paul Dale Wrote:  The other big difference between the two libraries is their size. The Intel library is large. Very large. It uses lots of look up tables to reduce functions to one of many low degree polynomial or rational approximations. This makes it very fast.

I guess I'll have to download and compile the Intel library to see how large it is. We only have 2 MB of flash, but if the library is that good, perhaps it will be worth the extra space.

(03-11-2014 10:33 PM)Paul Dale Wrote:  If you have the space, use the Intel library. You get a large suite of well tested fast functions. If you are tight for space, use decNumber and crib the transcendentals etc from the 34S project. You'll get a slightly larger set of functions that aren't as well tested or fast but which are tightly coded.


- Pauli

I guess we'll have to evaluate both and decide. Speed will be a major factor, since the idea is to be faster than userRPL, and I think that pushes towards decQuad. Availability of functions (equals faster development) pushes towards Intel, so it's a tie. We need to look at the size of the library to break the tie... if it fits, the Intel library will probably help get us there faster.

Thanks for the insight.
Claudio