sincordic.c

是codic算法实现Sin的浮点C程序

#include "headDefine.h"

double sinCordic(double theta) {
	
	int i;  		// for iteration
	int N = 8;  	// loop times 
					// 7 -> 0.01的误差；8->可以收敛；11 -> 0.001的误差

	double X[21] = {0.607253, 0};	// 11 = N + 1
	double Y[21] = {0};
	double result = 0;				// the return result
	double precision = 0.00001;		// the pricision of the radian

	int thetaQuadrant = 0;			// the quadrant of theta
	int S;							// 
	
	// get the (theta % (2 * PI)), [0, 2*PI]
	int quotient = floor(theta / (2 * PI));
	theta = theta - 2 * PI * quotient;
	
	// turn to the range: [-PI, PI]
	//if (theta > PI && theta <= 2 * PI) {
	//	theta = theta - 2 * PI;
	//}

	// judge the quadrant of theta, and transfer theta to the first quadrant
    if (theta >= 0 && theta <= PI/2) {          // 第一象限
        theta = theta;
        thetaQuadrant = 1;
	}
    else if (theta > PI/2 && theta <= PI) {      // 第二象限
        theta = PI - theta;
        thetaQuadrant = 2;
	}
	else if (theta >= PI && theta < PI / 2 * 3) {    // 第三象限
        theta = theta - PI;
        thetaQuadrant = 3;
	}
	else if (theta >= PI / 2 * 3 && theta < 2 * PI) {      // 第四象限
        theta = 2 * PI - theta;
        thetaQuadrant = 4;
	}
	

	if (theta == 0 || theta == PI/6 || (theta >= 0.785397 && theta <= 0.785398) || theta == PI/3 || theta == PI/2) {
		if (theta == 0)
			result = 0;
		else if (theta == PI/6)
			result = 0.5000;
		else if (theta >= 0.785397 && theta <= 0.785398)
			result = 0.70710678118655;
		else if (theta == PI/3)
			result = 0.86602540378444;
		else if (theta == PI/2)
			result = 1;

		if (thetaQuadrant == 1 || thetaQuadrant == 2)
			result = result;
		else
			result = -result;
	
	}
	else {
		// main iterations
		for (i = 0; i < N; i++) {
			// get the sign of S 
			// that is the clockwise or anticlockwise rotation
			if (theta > precision)
				S = 1;
			else if (theta < -precision)
				S = -1;
			else {
				break;
			}
			
			X[i + 1] = X[i] - S * Y[i] / pow(2, i);
			Y[i + 1] = Y[i] + S * X[i] / pow(2, i);
			theta = theta - S * atan(1 / pow(2, i));
		}

		if (thetaQuadrant == 1 || thetaQuadrant == 2)
			result = Y[i];
		else
			result = -Y[i];
	
	}

	return(result);
}