Sparky1039 0 Posted October 24, 2016 Report Share Posted October 24, 2016 (edited) I couldn't find anything in the documentation indicating that SB supports the C math library which has the POW(x,y) function. What I'm trying to do is compute this equation... y = 52080 x^-0.8754 (note X is an unsigned integer variable) It is a curve fit formula of a non-linear transform. My goal is to see how computationally intensive this is and if it's worth developing a look-up table as an alternative approach. The issue with the lookup table is the amount of memory I have available (both ROM or RAM). External RAM/EEPROM may work but the timing delay involved scanning a couple hundred points could be prohibitive. On the other hand perhaps someone has a better approach to efficiently compute this equation. Thanks Edited October 24, 2016 by Sparky1039 Quote Link to post Share on other sites

JorgeF 0 Posted October 28, 2016 Report Share Posted October 28, 2016 (edited) Hi I would not expect to find a math library for an 8 bit PIC with more than the 4 basic operations and even so only for integers. Floating point powers are a bit too hard for an 8 bit PIC. That is a job for a 16 or 32 bit PIC. Given that, I already faced such a chalenge in a real world application (a lab tool). But by looking at the forest rather than the tree, I end up with a PIC for raw data aquisition and a PC for the heavy processing. I've also seen another approach by someone else, an 8 bit PIC for data aquisition and a "Raspeberry Pi" for the heavy work (maths+storage+network). If you "really" need to use the PIC for the maths, than a mix of processing and data tables can do the trick. Remember your maths, in special logarithms and exponentiation. You can reduce the "pow" to product/quotient and the product/quotient to sum/subbtration. Also the floating point numbers can be reduced to fixed point integers to a given precision. This way you may be able to do the trick with only a logarithmic table. In terms of table sizes, I frequently manage to keep them in a controled size by simulating the problem in a spreadsheet and reducing the ranges and resolution to what is really needed for a given project. Another thing that helps in saving processing time is to keep in mind what kind of precision is "really" necessary for a given application. Just in case you need a quick refresh.... https://mathvault.ca/logarithm-theory/#scale HIH Best regards Jorge Edited October 28, 2016 by JorgeF Quote Link to post Share on other sites

Sparky1039 0 Posted November 24, 2016 Author Report Share Posted November 24, 2016 Thanks Jorge. After pondering the issues it became very obvious that it wasn't possible to do this kind of number crunching with a small 8-bit PIC. Exponentiation generates such enormous sized numbers that 64-bit variables are a must. Even if I could get the 8-bit PIC to deal with this math it would take equally large amounts of time to process it, completely negating the whole purpose of the exercise. Even a big lookup table would seen lightning fast in comparison. So that was the route I have taken, and by applying a binary tree search process it actually isn't so bad time wise. Cheers. Quote Link to post Share on other sites

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