Category : C Source Code
Archive   : CSRC2.ZIP
Filename : ATAN.C

 
Output of file : ATAN.C contained in archive : CSRC2.ZIP
/* atan - arctangent functions */

/*
functions used to compute the arctangent of two numbers (the sine term
and the cosine term.

This stolen from the c floating point library at yale cs dept vax.

Based on Hart & Cheney (#5077 , 19.56D)
*/

static double sq2p1 = 2.414213562373095048802e0;
static double sq2m1 = 0.414213562373095048802e0;
static double pio2 = 1.570796326794896619231e0;
static double pio4 = 0.785398163397448309615e0;
static double p4 = 0.161536412982230228262e2;
static double p3 = 0.268425481955039737941e3;
static double p2 = 0.115302935154048501154e4;
static double p1 = 0.178040631643319697105e4;
static double p0 = 0.896785974036638619599e3;
static double q4 = 0.589569705084446222279e2;
static double q3 = 0.536265374031215315104e3;
static double q2 = 0.166678381488163371845e4;
static double q1 = 0.207933497444540981287e4;
static double q0 = 0.896785974036638619624e3;

static double xatan(arg)

double arg;
{
double argsq;
double value;

argsq = arg*arg;
value = ((((p4*argsq+p3)*argsq+p2)*argsq+p1)*argsq+p0);
value = value/(((((argsq+q4)*argsq+q3)*argsq+q2)*argsq+q1)*argsq+q0);
return(value*arg);
}

/* satan reduces range to single quadrant and calls xatan to do work */

static double satan(arg)

double arg;
{
if (arg < sq2m1)
return(xatan(arg));
else
if (arg > sq2p1)
return(pio2-xatan(1.0/arg));
else
return(pio4+xatan((arg-1.0)/(arg+1.0)));
}

/* atan2 figures out the quadrant and returns correct atan */

double atan2(arg2,arg1)

double arg2,arg1;
{
if ((arg1+arg2) == arg1)
{
if (arg1 == 0.0) return(0.0);
if (arg1 > 0.0)
return(pio2);
else
return(-pio2);
}
else
{
if (arg2 < 0.0)
{
if (arg1 >= 0.0)
return(pio2+pio2-satan(-arg1/arg2));
else
return(-pio2-pio2+satan(arg1/arg2));
}
else
{
if (arg1 > 0.0)
return(satan(arg1/arg2));
else
return(-satan(-arg1/arg2));
} } }


  3 Responses to “Category : C Source Code
Archive   : CSRC2.ZIP
Filename : ATAN.C

  1. Very nice! Thank you for this wonderful archive. I wonder why I found it only now. Long live the BBS file archives!

  2. This is so awesome! 😀 I’d be cool if you could download an entire archive of this at once, though.

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