Sin and Cos in Spin

crgwbr

Are there any objects already released that do Sin and Cos calculations.· If not, I could just use a floating point co-processor; I would just rather do it with software.

Thanks,
crgwbr

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asterick

There is a SIN table in the rom, it's fixed point, so you can just convert it to floating point by sign extending it and then dividing it by 32768.0. I forget where it's located... check the manual

Beau Schwabe

crgwbr,
·
Here are a few routines that can be incorporated into any object.· Keep in mind, that the Propeller contains a ROM table for 1/4 of SIN.· Based on your degree value you either flip and/or mirror the data to get the proper quadrant. (The routine below does this for you).· The·SIN·angle is represented as a 13-bit value, while the returned value is represented as a signed 16-bit value.
·

PUB DEG2PROP(Deg)               'Convert Deg to 13-bit Propeller angle
    Result := (Deg * 1024)/45
 
PUB Cos(angle)                  'Cos angle is 13-bit ; Returns a 16-bit signed value
    Result := sin(angle + $800)
 
PUB Sin(angle)                  'Sin angle is 13-bit ; Returns a 16-bit signed value
    Result := angle << 1 & $FFE
    if angle & $800
       Result := word[noparse][[/noparse]$F000 - Result]
    else
       Result := word[noparse][[/noparse]$E000 + Result]
    if angle & $1000
       -Result

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

crgwbr

Thanks Beau,

So to use those routines, I would use something like:

PropAng := DEG2PROP(270)
CosAng := Cos(PropAng)
SinAng := Sin(PropAng)

Would this work?

Thanks Again,
crgwbr

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Tracy Allen

That's right, or you can encapulate it as:

CosAng := Cos(DEG2PROP(270))
SinAng := Sin(DEG2PROP(270))



Here is an alternaive method to code the Sin routine that resolves the 4 quadrants using a case statement:

PRI Sin(pangle) | q                           ' prop angle is 0 to 2^13 (0 to 8191) for 0 to 360 degrees
  q := pangle >> 11                            ' quadrant is 2 highest bits
  result := (pangle & $7ff) << 1             ' 0 to 90- degrees, 11 bits, times two for word offset into sine table
  case q                                           ' result by quadrant, lookup in HUB SINE table
    0 : result := word[noparse][[/noparse]$E000 + result]                     
    1 : result := word[noparse][[/noparse]$F000 - result]
    2 : result := -word[noparse][[/noparse]$E000 + result]
    3 : result := -word[noparse][[/noparse]$F000 - result]
  return

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Tracy Allen
www.emesystems.com

crgwbr

Thanks Tracy

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Graham Stabler

If you are interested in assembly or just high speed then I wrote a cordic algorithm that will compute R.Sin(theta) and R.Cos(theta) simultaneously in no time at all, it uses Cordic:

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

My intention was to releas the code in two forms, assembly to be inserted in to other assembly programs and as a high speed cordic object. The cordic method can be used for other things like sqrt and 1/x so it could sit in a cog and just churn out what was asked of it. I just need time to sit down and put it together but after my move I am still no quite unpacked.

I did release a basic demo program here though:

http://forums.parallax.com/forums/default.aspx?f=25&m=150119

Graham

Graham Stabler

Oops, you said spin

crgwbr

Sorry Graham, but I'm haveing enough trouble with learning spin. Not quite ready to learn assembly.

Thanks Anyway,
crgwbr

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