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parag
parag
Associate III
February 2, 2011
Question

How to calculate tan angles..

  • February 2, 2011
  • 7 replies
  • 1982 views
Posted on February 02, 2011 at 22:12

How to calculate tan angles..

    This topic has been closed for replies.

    7 replies

    picguy2
    picguy2
    Associate III
    May 17, 2011
    Posted on May 17, 2011 at 14:23

    Use the tan(x) from your C compiler.

    madhu13
    madhu13
    Associate III
    May 17, 2011
    Posted on May 17, 2011 at 14:23

    add ''math.h'' lib and use tan(x) function.

      parag
      paragAuthor
      Associate III
      May 17, 2011
      Posted on May 17, 2011 at 14:23

      Thanks a lot guys.

      @neil: I am using Ride7 and working on STM32F103ZE. Do you know how to add that floating library file in it?? is it available for this controller?. Thanks a lot for help.

      Andrew Neil
      Andrew Neil
      Super User
      May 17, 2011
      Posted on May 17, 2011 at 14:23

      ''add 'math.h' lib''

       

      Note that math.h is

      not

        a library - it is just a header file!

      In addition to #include-ing math.h, you will also have to add the appropriate floating-point lirary/libraries to your project.

      For details, see the documentation for your particular toolset.

      Note that some free/restricted toolset versions may not allow use of floating point

      picguy2
      picguy2
      Associate III
      May 17, 2011
      Posted on May 17, 2011 at 14:23

      Integer vs. floating point makes a BIG difference in execution time.  My DTMF decode went from 10 milliseconds to 0.6 milliseconds.  

      This was for a 100 sample Goertzel algorithm performing sums and power calculation using integer arithmetic returning a signed 64-bit integer.  I used 16 different frequencies -- the basic 8(*) and their second harmonics.  C code converted that to 32-bit fp.  Column/row selection used fp to pick a winner that had to be 3x the sum of the other three items.  Sum of all 8 harmonics had to be a factor of 3 or 4 less than the winning row value.

      (*) that included the almost never present ABCD column to the right of 369#.
      John F.
      John F.
      Associate III
      May 17, 2011
      Posted on May 17, 2011 at 14:23

      If you want to learn more about methods and approximations, have a look at the book ''Math toolkit for real-time programming'' by Jack W. Crenshaw.

      Andrew Neil
      Andrew Neil
      Super User
      May 17, 2011
      Posted on May 17, 2011 at 14:23

      Note that floating-point has a very significantly greater overhead (both code size and execution time) than integer maths - therefore you should think very carefully indeed whether you really  need floating point in your application.

      This is one reason why many (most?) embedded toolchains do not include floating-point by default.

      In most cases, it is easy enough to scale you values so that you can do everything in integer maths; eg, instead of processing 3.3V as a floating-point number, think of it as 3300mV - an integer!

      You can choose any scaling factor that is convenient to your particular application.

      Functions such as tan() can be implemented as lookup tables,  or integer implementations - so-called ''fixed point'' - are available.

      eg, CORDIC algorithms: 

      http://en.wikipedia.org/wiki/CORDIC

      So, try it first using floating-point; but be aware that this may give you code-size and/or performance issues - so be prepared to explore the alternatives...
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