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"
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#include "fixed_math.hpp"
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#define MAXBITS 15
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static float invGain1;
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static float atanTable[MAXBITS];
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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
Feb 7 '07
12 9601 RedSon 5,000
Recognized Expert Expert
Would your professor not give limited permission under an academic free license for us to view his/her code?
MMcCarthy 14,534
Recognized Expert Moderator MVP
Would your professor not give limited permission under an academic free license for us to view his/her code?
It would have to be by PM if he/she does as it cannot be publicly published on the site.
Mary
finally i can solved the errors in my program , but the counting result is wrong.Take a look in my program , where is my mistakes?
*ps i had count arctan using CORDIC in floating point and i use the same method when counting it in fixed point only in here i use Q15 class. i`m bold-ing the font which is different from my floating point program and Italic font is what i use for the floating point. -
#include <vcl.h>
-
#pragma hdrstop
-
-
-
#include "Unit1.h"
-
#include "math.h"
-
#include "fixed_math.hpp"
-
#define MAXBITS 15
-
//---------------------------------------------------------------------------
-
#pragma package(smart_init)
-
#pragma resource "*.dfm"
-
TForm1 *Form1;
-
//---------------------------------------------------------------------------
-
__fastcall TForm1::TForm1(TComponent* Owner)
-
: TForm(Owner)
-
{
-
}
-
//---------------------------------------------------------------------------
- static float atanTable[MAXBITS];
- static double atanTable[MAXBITS];
-
-
-
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;
-
double t = 1;
-
int s;
-
for (s = 0; s < MAXBITS; ++s)
-
{
-
atanTable[s] = atan(t);
-
t /= 2;
-
}
-
-
}
-
-
-
/* CORDIC m=1, y-->0 */
-
-
-
- Q15 cordic(Q15* x0, Q15* y0, Q15* z0, Q15 vecmode)
- void cordic(double* x0, double* y0, double* z0, double vecmode)
-
{
-
-
short t;
-
Q15 x, y, z;
-
double t;
-
double x, y, z;
-
-
int s;
-
-
t = 1.0f;
-
x = *x0; y = *y0; z = *z0;
-
-
for (s = 0; s < MAXBITS; ++s)
-
{
-
-
Q15 x1;
-
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 - Q15(atanTable[s]);
-
}
-
else
-
{
-
Q15 x1 = x + y>>t;
-
y = y - x>>t;
-
z = z + Q15(atanTable[s]);
-
}
-
-
x=x1;
-
t /= 2;
-
}
-
-
*x0 = x;
-
*y0 = y;
-
*z0 = z;
-
-
return z;
-
}
-
-
- Q15 atanCordic(Q15 a)
- double atanCordic(double a)
-
{
-
/* domain: all a */
- Q15 x = 1.0f;
-
Q15 z = 0.0f;
-
double x = 1;
-
double z = 0;
-
cordic(&x, &a, &z, 0.0f);
-
return z;
-
}
-
-
void __fastcall TForm1::Button1Click(TObject *Sender)
-
{
-
AnsiString buf;
-
float x;
-
float y;
-
double v,y,r;
-
double x;
-
-
-
initCordic();
-
-
for (x=0.0;x<=1.0;x=x+0.1)
-
{
-
-
Q15 v = atanCordic(x);
-
v = atanCordic(x);
-
y = 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));
-
-
}
-
-
-
}
-
//---------------------------------------------------------------------------
-
-
-
-
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