CORDIC arctan function with fixed point (i`m using Q15 format)

[astri]

i`m doing my thesis comparing CORDIC with polynomial in counting arctan with fixed point. I`m using Q15 format now. I`m using this site CORDIC arctan as a referenced when making with floating point. The problem there`s a lot of error when i try to make it with fixed point.

this is my program

#include "Unit1.h"
#include "math.h"
#include "fixed_math.hpp"
#define MAXBITS 15
static  float invGain1;
static  float atanTable[MAXBITS];
static  float gain1Cordic();
 
 
void initCordic()
{
    /* must call this first to initialise the constants.
     * of course, here i use the maths library, but the
     * values would be precomputed.
     */
    float t = 1.0f;
    int i;
    for (i = 0; i < MAXBITS; ++i)
    {
        atanTable[i] = atan(t);
        t /= 2;
    }
 
    /* set constants */
    invGain1 = 1/gain1Cordic();
}
 
/* CORDIC m=1, y-->0 */
 
Q15 cordic(Q15 &x0, Q15 &y0, Q15 &z0, Q15 vecmode)
{
 
    short t;
    Q15 x, y, z;
    int i;
 
    t = 1.0f;
    x = x0; y = y0; z = z0;
 
    for (i = 0; i < MAXBITS; ++i)
    {
 
        double x1;
 
        if (vecmode >= 0.0f && y < vecmode || vecmode<0.0f  && z >= 0.0f)
        {
            Q15 x1 = x - y>>t;
            y = y + x>>t;
            z = z - atanTable[i];
        }
        else
        {
            Q15 x1 = x + y>>t;
            y = y - x>>t;
            z = z + atanTable[i];
        }
 
         x = x1;
        t /= 2;
    }
 
    x0 = x;
    y0 = y;
    z0 = z;
 
}
 
 
static  float gain1Cordic()
{
    /* compute gain by evaluating cos(0) without inv gain */
    float x, y, z;
 
    x = 1;
    y = 0;
    z = 0;
    cordic(&x, &y, &z, 1.0f);
    return x;
}
 
Q15 atanCordic(Q15 a)
{
    /* domain: all a */
    Q15 x = 1.0f;
    Q15 z = 0.0f;
    cordic(&x, &a, &z, 0.0f);
    return z;
}
 
void __fastcall TForm1::Button1Click(TObject *Sender)
{
    AnsiString buf;
    float x;
    float v,c;
 
 
    initCordic();
 
    for (x=0.0;x<=1.0;x=x+0.1)
    {
 
       Q15 y = atanCordic(x);
        v = atan(x);
 
 
        Memo1->Lines->Add(buf.sprintf("%5.2f\n", x));
        Memo2->Lines->Add(buf.sprintf("%10.6f\n",Q15ToShort(v)/32768.0));
        Memo3->Lines->Add(buf.sprintf("%10.6f\n",Q15ToShort(y)/32768.0));
 
    }
 
 
}
 
 

anyone can help?

if you have suggestion about making it with others rather than Q15 format, as long it is fixed point, it is very usefull to

[sicarie]

astri-

I'm not sure if I can help with the logic of your program (that's a little over my head!), but it's more than likely that I or someone else browsing through would be able to help you with the error messages that you are getting, if you could post those.

sicarie

[RedSon]

Can you give us an example of your input and output. What kind of error are you getting?

[astri]

i`m bolding the font ONLY for error messages(ignore the warning) in my program

 
#include "Unit1.h"
#include "math.h"
#include "fixed_math.hpp"
#define MAXBITS 15
 
static  float invGain1;
static  float atanTable[MAXBITS];
static  float gain1Cordic();
 
 
void initCordic()
{
    /* must call this first to initialise the constants.
     * of course, here i use the maths library, but the
     * values would be precomputed.
     */
    float t = 1.0f;
    int i;
    for (i = 0; i < MAXBITS; ++i)
    {
        atanTable[i] = atan(t);
        t /= 2;
    }
 
    /* set constants */
    invGain1 = 1/gain1Cordic();
}
 
/* CORDIC m=1, y-->0 */
 
Q15 cordic(Q15 &x0, Q15 &y0, Q15 &z0, Q15 vecmode)
{
 
    short t;
    Q15 x, y, z;
    int i;
 
    t = 1.0f;
    x = x0; y = y0; z = z0;
 
    for (i = 0; i < MAXBITS; ++i)
    {
 
        double x1;
 
        if (vecmode >= 0.0f && y < vecmode || vecmode<0.0f  && z >= 0.0f)
        {
            Q15 x1 = x - y>>t;
            y = y + x>>t;
            z = z - atanTable[i];
        }
        else
        {
            Q15 x1 = x + y>>t;
            y = y - x>>t;
            z = z + atanTable[i];
        }
 
         x = x1;
        t /= 2;
    }
 
    x0 = x;
    y0 = y;
    z0 = z;
 
}
 
 
static  float gain1Cordic()
{
    /* compute gain by evaluating cos(0) without inv gain */
    float x, y, z;
 
    x = 1;
    y = 0;
    z = 0;
    cordic(&x, &y, &z, 1.0f);-->THE MAIN PROBLEM, 
    return x;                     the error messages repeated so much in this line
}
 
Q15 atanCordic(Q15 a)
{
    /* domain: all a */
    Q15 x = 1.0f;
    Q15 z = 0.0f;
    cordic(&x, &a, &z, 0.0f);
    return z;
}
 
void __fastcall TForm1::Button1Click(TObject *Sender)
{
    AnsiString buf;
    float x;
    float v,c;
 
 
    initCordic();
 
    for (x=0.0;x<=1.0;x=x+0.1)
    {
 
       Q15 y = atanCordic(x);
        v = atan(x);
 
        Memo1->Lines->Add(buf.sprintf("%5.2f\n", x));
        Memo2->Lines->Add(buf.sprintf("%10.6f\n",y));
        Memo3->Lines->Add(buf.sprintf("%10.6f\n",v));
 
 
    }
 
 
}
 
 

this is my error messages

[code]
[C++ errorー] Unit1.cpp(67): E2015 'Q15:: operator -(const Q15 &) const' and 'Q15:: operator -(const Q30 &) const' classification are ambiguous retrieval
[C++ errorー] Unit1.cpp(73): E2015 'Q15:: operator +(const Q15 &) const' and 'Q15:: operator +(const Q30 &) const' classification are ambigous retrieval
[C++ error ー] Unit1.cpp(76): E2015 'Q15::Q15(const short)' and 'Q15::Q15(const float)' classification are ambigous retrieval
[C++ warning] Unit1.cpp(84): W8070 return function value
[C++ warning] Unit1.cpp(95): W8030 'x0' parameter(cordi c(Q15 &,Q15 &,Q15 &,Q15))is used as temporarily variables
[C++ error] Unit1.cpp(95): E2064 'Q15 &' cant initialized as 'float *'
[C++ error] Unit1.cpp(95): E2342 'x0'parameter is define as Q15 & so it cant be change to float *
[C++ warning] Unit1.cpp(95): W8030 'y0' parameter(cordi c(Q15 &,Q15 &,Q15 &,Q15))is used as temporarily variables
[C++ error] Unit1.cpp(95): E2064 'Q15 &' cant initialized as 'float *'
[C++ error] Unit1.cpp(95): E2342 'y0'b parameter is Q15 & type and cant be change to float *
[C++ warning] Unit1.cpp(95): W8030 'z0' parameters(cord ic(Q15 &,Q15 &,Q15 &,Q15))is used as temporarily variables
[C++ error] Unit1.cpp(95): E2064 'Q15 &' cant initialized as 'float *'
[C++ error] Unit1.cpp(95): E2342 'z0' parameter is Q15 & type and cant be change to float *
[C++ warning] Unit1.cpp(97): W8004 'z' subtituted value is not use
[C++ warning] Unit1.cpp(97): W8004 'y' subtituted value is not use [C++ warning] Unit1.cpp(104): W8030 'x0' parameter(cordi c(Q15 &,Q15 &,Q15 &,Q15))is used as temporarily variables
[C++ error] Unit1.cpp(104): E2064 'Q15 &' is 'Q15 *' cant be initialized
[C++ error] Unit1.cpp(104): E2342 'x0' parameters is Q15 & type and cant be change to Q15 *
[C++ warning] Unit1.cpp(104): W8030 'y0' parameters(cord ic(Q15 &,Q15 &,Q15 &,Q15))is used as temporarily variables
[C++ error] Unit1.cpp(104): E2064 'Q15 &' is 'Q15 *' cant be initialized
[C++ error] Unit1.cpp(104): E2342 'y0' parameters is Q15 & type and cant be change to Q15 *
[C++ warning] Unit1.cpp(104): W8030 'z0' パラメータ(cordic(Q1 5 &,Q15 &,Q15 &,Q15))is used as temporarily variables
[C++ warning] Unit1.cpp(104): E2064 'Q15 &' は 'Q15 *' cant be initialized
[C++ error] Unit1.cpp(104): E2342 'z0' parameters is Q15 & type and cant be change to Q15 *



i`m thinking the main problem in my program is because i`m trying to use fixed point (its about the data type). I dont really understand that much.



*ps i`m using c++builder for japanese so the error message output is in japanese , i`m translating by myself to english (so if it`s sound weird please correct it or ask me)

[horace1]

the function definition of cordic() sepcifies that the formal parameters and return type are Q15

Q15 cordic(Q15 &x0, Q15 &y0, Q15 &z0, Q15 vecmode)
 

you call it with actual parameters of type float

static  float gain1Cordic()
{
    /* compute gain by evaluating cos(0) without inv gain */
    float x, y, z;
 
    x = 1;
    y = 0;
    z = 0;
    cordic(&x, &y, &z, 1.0f);-->THE MAIN PROBLEM, 
    return x;                     the error messages repeated so much in this line
}
 

where did you get the Q15 fixed point library from?

[astri]

the function definition of cordic() sepcifies that the formal parameters and return type are Q15

Q15 cordic(Q15 &x0, Q15 &y0, Q15 &z0, Q15 vecmode)
 

you call it with actual parameters of type float

static  float gain1Cordic()
{
    /* compute gain by evaluating cos(0) without inv gain */
    float x, y, z;
 
    x = 1;
    y = 0;
    z = 0;
    cordic(&x, &y, &z, 1.0f);-->THE MAIN PROBLEM, 
    return x;                     the error messages repeated so much in this line
}
 

where did you get the Q15 fixed point library from?

my professor make it by himself the library, i included it in fixed_math.hpp

[RedSon]

Can you post the .hpp file with your professors code in it? If it is large consider using the website mediafire.com to upload it and give us the link to it. Also, when you translate error messages, please try to translate word for word. What I mean is don't worry about changing the grammar and word order so that is makes sense in english. We can still get the meaning even though it may not look right, and that way there is less loss in translation. :)

[MMcCarthy]

Can you post the .hpp file with your professors code in it? If it is large consider using the website mediafire.com to upload it and give us the link to it. Also, when you translate error messages, please try to translate word for word. What I mean is don't worry about changing the grammar and word order so that is makes sense in english. We can still get the meaning even though it may not look right, and that way there is less loss in translation. :)

Sorry guys I've already told the OP they can't as the code is copyrighted.

[RedSon]

The professor's code is copyrighted? Or the CORDIC code?

[astri]

The professor's code is copyrighted? Or the CORDIC code?

sorry my professor code is copyrighted