/**
* Compute cosine in the first quadrant by subtracting input from PI/2 and
* then calling sinQ. This is more accurate as the input approaches PI/2.
* @param xa number from which cosine is requested
* @param xb extra bits for x (may be 0.0)
* @return cos(xa + xb)
*/
public static double Quadrant(double xa, double xb)
{
double pi2a = 1.5707963267948966;
double pi2b = 6.123233995736766E-17;
double a = pi2a - xa;
double b = -(a - pi2a + xa);
b += pi2b - xb;
return(Sine.Quadrant(a, b));
}
/**
* Compute tangent (or cotangent) over the first quadrant. 0 < x < pi/2
* Use combination of table lookup and rational polynomial expansion.
* @param xa number from which sine is requested
* @param xb extra bits for x (may be 0.0)
* @param cotanFlag if true, compute the cotangent instead of the tangent
* @return tan(xa+xb) (or cotangent, depending on cotanFlag)
*/
public static double Quadrant(double xa, double xb, bool cotanFlag)
{
int idx = (int)((xa * 8.0) + 0.5);
double epsilon = xa - BitOps.EIGHTHS[idx]; //idx*0.125;
// Table lookups
double sintA = Sine.SINE_TABLE_A[idx];
double sintB = Sine.SINE_TABLE_B[idx];
double costA = Cosine.COSINE_TABLE_A[idx];
double costB = Cosine.COSINE_TABLE_B[idx];
// Polynomial eval of sin(epsilon), cos(epsilon)
double sinEpsA = epsilon;
double sinEpsB = Sine.Poly(epsilon);
double cosEpsA = 1.0;
double cosEpsB = Cosine.Poly(epsilon);
// Split epsilon xa + xb = x
double temp = sinEpsA * BitOps.HEX_40000000;
double temp2 = (sinEpsA + temp) - temp;
sinEpsB += sinEpsA - temp2;
sinEpsA = temp2;
/* Compute sin(x) by angle addition formula */
/* Compute the following sum:
*
* result = sintA + costA*sinEpsA + sintA*cosEpsB + costA*sinEpsB +
* sintB + costB*sinEpsA + sintB*cosEpsB + costB*sinEpsB;
*
* Ranges of elements
*
* xxxtA 0 PI/2
* xxxtB -1.5e-9 1.5e-9
* sinEpsA -0.0625 0.0625
* sinEpsB -6e-11 6e-11
* cosEpsA 1.0
* cosEpsB 0 -0.0625
*
*/
//result = sintA + costA*sinEpsA + sintA*cosEpsB + costA*sinEpsB +
// sintB + costB*sinEpsA + sintB*cosEpsB + costB*sinEpsB;
//result = sintA + sintA*cosEpsB + sintB + sintB * cosEpsB;
//result += costA*sinEpsA + costA*sinEpsB + costB*sinEpsA + costB * sinEpsB;
double a = 0;
double b = 0;
// Compute sine
double t = sintA;
double c = a + t;
double d = -(c - a - t);
a = c;
b = b + d;
t = costA * sinEpsA;
c = a + t;
d = -(c - a - t);
a = c;
b = b + d;
b = b + sintA * cosEpsB + costA * sinEpsB;
b = b + sintB + costB * sinEpsA + sintB * cosEpsB + costB * sinEpsB;
double sina = a + b;
double sinb = -(sina - a - b);
// Compute cosine
a = b = c = d = 0.0;
t = costA * cosEpsA;
c = a + t;
d = -(c - a - t);
a = c;
b = b + d;
t = -sintA * sinEpsA;
c = a + t;
d = -(c - a - t);
a = c;
b = b + d;
b = b + costB * cosEpsA + costA * cosEpsB + costB * cosEpsB;
b = b - (sintB * sinEpsA + sintA * sinEpsB + sintB * sinEpsB);
double cosa = a + b;
double cosb = -(cosa - a - b);
if (cotanFlag)
{
double tmp;
tmp = cosa; cosa = sina; sina = tmp;
tmp = cosb; cosb = sinb; sinb = tmp;
}
/* estimate and correct, compute 1.0/(cosa+cosb) */
/*
* double est = (sina+sinb)/(cosa+cosb);
* double err = (sina - cosa*est) + (sinb - cosb*est);
* est += err/(cosa+cosb);
* err = (sina - cosa*est) + (sinb - cosb*est);
*/
// f(x) = 1/x, f'(x) = -1/x^2
double est = sina / cosa;
/* Split the estimate to get more accurate read on division rounding */
temp = est * BitOps.HEX_40000000;
double esta = (est + temp) - temp;
double estb = est - esta;
temp = cosa * BitOps.HEX_40000000;
double cosaa = (cosa + temp) - temp;
double cosab = cosa - cosaa;
//double err = (sina - est*cosa)/cosa; // Correction for division rounding
double err = (sina - esta * cosaa - esta * cosab - estb * cosaa - estb * cosab) / cosa; // Correction for division rounding
err += sinb / cosa; // Change in est due to sinb
err += -sina * cosb / cosa / cosa; // Change in est due to cosb
if (xb != 0.0)
{
// tan' = 1 + tan^2 cot' = -(1 + cot^2)
// Approximate impact of xb
double xbadj = xb + est * est * xb;
if (cotanFlag)
{
xbadj = -xbadj;
}
err += xbadj;
}
return(est + err);
}
