#include <stdio.h> | |
#include <stdlib.h> | |
#include <math.h> | |
float atan2_approximation1(float y, float x); | |
float atan2_approximation2(float y, float x); | |
int main() | |
{ | |
float x = 1; | |
float y = 0; | |
for( y = 0; y < 2*M_PI; y+= 0.1 ) | |
{ | |
for(x = 0; x < 2*M_PI; x+= 0.1) | |
{ | |
printf("atan2 for %f,%f: %f \n", y, x, atan2(y, x)); | |
printf("approx1 for %f,%f: %f \n", y, x, atan2_approximation1(y, x)); | |
printf("approx2 for %f,%f: %f \n \n", y, x, atan2_approximation2(y, x)); | |
getch(); | |
} | |
} | |
return 0; | |
} | |
float atan2_approximation1(float y, float x) | |
{ | |
//http://pubs.opengroup.org/onlinepubs/009695399/functions/atan2.html | |
//Volkan SALMA | |
const float ONEQTR_PI = M_PI / 4.0; | |
const float THRQTR_PI = 3.0 * M_PI / 4.0; | |
float r, angle; | |
float abs_y = fabs(y) + 1e-10f; // kludge to prevent 0/0 condition | |
if ( x < 0.0f ) | |
{ | |
r = (x + abs_y) / (abs_y - x); | |
angle = THRQTR_PI; | |
} | |
else | |
{ | |
r = (x - abs_y) / (x + abs_y); | |
angle = ONEQTR_PI; | |
} | |
angle += (0.1963f * r * r - 0.9817f) * r; | |
if ( y < 0.0f ) | |
return( -angle ); // negate if in quad III or IV | |
else | |
return( angle ); | |
} | |
#define PI_FLOAT 3.14159265f | |
#define PIBY2_FLOAT 1.5707963f | |
// |error| < 0.005 | |
float atan2_approximation2( float y, float x ) | |
{ | |
if ( x == 0.0f ) | |
{ | |
if ( y > 0.0f ) return PIBY2_FLOAT; | |
if ( y == 0.0f ) return 0.0f; | |
return -PIBY2_FLOAT; | |
} | |
float atan; | |
float z = y/x; | |
if ( fabs( z ) < 1.0f ) | |
{ | |
atan = z/(1.0f + 0.28f*z*z); | |
if ( x < 0.0f ) | |
{ | |
if ( y < 0.0f ) return atan - PI_FLOAT; | |
return atan + PI_FLOAT; | |
} | |
} | |
else | |
{ | |
atan = PIBY2_FLOAT - z/(z*z + 0.28f); | |
if ( y < 0.0f ) return atan - PI_FLOAT; | |
} | |
return atan; | |
} |
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In my (somewhat limited but concise) testing on both a very fast Gen 7 Xeon and an STM32F4 (w/FPU) ARM micro show On STM32F4 On the Xeon under Windows with MSVC Thanks for this snip, very handy! |
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For anyone looking at this in the future, this function was first referenced on an Apple mailing list in 2005 that's not in their current archives (but it is on the wayback machine!). It was a derivative of a similar function form 1999 which can be found here. That function was in the |
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Can I use and publish this under Apache 2 license with proper attribution? It would be for graphhopper