Hello, I have to implement atan2 on a dsPIC30F and would like to do that in fixed point for reasonable performance. Does someone already did that? Thanks, -- Eric Meurville
C code for fixed point atan2
Started by ●January 20, 2005
Reply by ●January 20, 20052005-01-20
Reply by ●January 21, 20052005-01-21
Thanks for the link but the code proposed uses floats and I would perform the computation with integers. EMe. Nithin wrote:> Hi > You may want to look a this > http://dspguru.com/comp.dsp/tricks/alg/fxdatan2.htm > > -Nithin >
Reply by ●January 21, 20052005-01-21
Hi Eric, Look again. The example code may use floats, but the title is "fixed point atan2 with self-normalisation". If you recast the numbers as fixed point values it works just fine. Regards, Steve Eric Meurville wrote:> Thanks for the link but the code proposed uses floats and I would > perform the computation with integers. > > EMe. > > Nithin wrote: > >> Hi >> You may want to look a this >> http://dspguru.com/comp.dsp/tricks/alg/fxdatan2.htm >> >> -Nithin >>
Reply by ●January 21, 20052005-01-21
Steve Underwood wrote:> Hi Eric, > > Look again. The example code may use floats, but the title is "fixed > point atan2 with self-normalisation". If you recast the numbers asfixed> point values it works just fine. > > Regards, > Steve > > > Eric Meurville wrote: > > > Thanks for the link but the code proposed uses floats and I would > > perform the computation with integers. > > > > EMe. > > > > Nithin wrote: > > > >> Hi > >> You may want to look a this > >> http://dspguru.com/comp.dsp/tricks/alg/fxdatan2.htm > >> > >> -Nithin > >>if you simply recast everything as integers, won't coeff_1 =0? and what do you do with 1e-10?
Reply by ●January 21, 20052005-01-21
I agree, this code is definetely floating point. Nevertheless, its performance on dsPIC30F is 3 times better than Microchip native math library. bungalow_steve@yahoo.com wrote:> Steve Underwood wrote: > >>Hi Eric, >> >>Look again. The example code may use floats, but the title is "fixed >>point atan2 with self-normalisation". If you recast the numbers as > > fixed > >>point values it works just fine. >> >>Regards, >>Steve >> >> >>Eric Meurville wrote: >> >> >>>Thanks for the link but the code proposed uses floats and I would >>>perform the computation with integers. >>> >>>EMe. >>> >>>Nithin wrote: >>> >>> >>>>Hi >>>>You may want to look a this >>>>http://dspguru.com/comp.dsp/tricks/alg/fxdatan2.htm >>>> >>>>-Nithin >>>> > > > if you simply recast everything as integers, won't coeff_1 =0? and what > do you do with 1e-10? >-- Eric Meurville
Reply by ●January 21, 20052005-01-21
bungalow_steve@yahoo.com wrote:> Steve Underwood wrote: > >>Hi Eric, >> >>Look again. The example code may use floats, but the title is "fixed >>point atan2 with self-normalisation". If you recast the numbers as > > fixed > >>point values it works just fine. >> >>Regards, >>Steve >> >> >>Eric Meurville wrote: >> >> >>>Thanks for the link but the code proposed uses floats and I would >>>perform the computation with integers. >>> >>>EMe. >>> >>>Nithin wrote: >>> >>> >>>>Hi >>>>You may want to look a this >>>>http://dspguru.com/comp.dsp/tricks/alg/fxdatan2.htm >>>> >>>>-Nithin >>>> > > > if you simply recast everything as integers, won't coeff_1 =0? and what > do you do with 1e-10? >Who said anything about using integers. I said fixed point. You don't even have to think about the 1e-10. A comment tells you why it is there, and it is, therefore, trivial to eliminate it with a bit of logic. The logic doesn't work so well with floats, which I guess is why the original is kludged in that way. Regards, Steve
Reply by ●January 21, 20052005-01-21
Steve Underwood wrote:> bungalow_steve@yahoo.com wrote: > > Steve Underwood wrote: > > > >>Hi Eric, > >> > >>Look again. The example code may use floats, but the title is"fixed> >>point atan2 with self-normalisation". If you recast the numbers as > > > > fixed > > > >>point values it works just fine. > >> > >>Regards, > >>Steve > >> > >> > >>Eric Meurville wrote: > >> > >> > >>>Thanks for the link but the code proposed uses floats and I would > >>>perform the computation with integers. > >>> > >>>EMe. > >>> > >>>Nithin wrote: > >>> > >>> > >>>>Hi > >>>>You may want to look a this > >>>>http://dspguru.com/comp.dsp/tricks/alg/fxdatan2.htm > >>>> > >>>>-Nithin > >>>> > > > > > > if you simply recast everything as integers, won't coeff_1 =0? andwhat> > do you do with 1e-10? > > > > Who said anything about using integers. I said fixed point. You don't> even have to think about the 1e-10. A comment tells you why it isthere,> and it is, therefore, trivial to eliminate it with a bit of logic.The> logic doesn't work so well with floats, which I guess is why the > original is kludged in that way. > > Regards, > SteveThere is a fixed point data type in C?
Reply by ●January 21, 20052005-01-21
Microchip might be implementing more terms in the polynomial, I suspect if you implemented the code in integer math on the dsPIC the entire function would execute in less time then a single floating point add. If I remember correctly the integer divide is the killer, 18 cycles, but even with that, your talking at most 25-30 cycles for the entire integer algorithm compared with over 100 cycles for a single floating addition.
Reply by ●January 21, 20052005-01-21
bungalow_steve@yahoo.com wrote: ...> There is a fixed point data type in C?Fixed-point is at worst integer scaled by shifts. Compilers for some processors that have fixed-point hardware do support a fixed-point type. Without that, either do the job in assembler or write C-callable assembly routines for best execution speed. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
