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lightning-sunbird  0.9+nobinonly
Functions | Variables
s_atan.c File Reference
#include "fdlibm.h"

Go to the source code of this file.

Functions

double fd_atan (double x)

Variables

static double atanhi []
static double atanlo []
static double aT []
static double one = 1.0
static double really_big = 1.0e300

Function Documentation

double fd_atan ( double  x)

Definition at line 126 of file s_atan.c.

{
        fd_twoints u;
       double w,s1,s2,z;
       int ix,hx,id;

        u.d = x;
       hx = __HI(u);
       ix = hx&0x7fffffff;
       if(ix>=0x44100000) { /* if |x| >= 2^66 */
            u.d = x;
           if(ix>0x7ff00000||
              (ix==0x7ff00000&&(__LO(u)!=0)))
              return x+x;          /* NaN */
           if(hx>0) return  atanhi[3]+atanlo[3];
           else     return -atanhi[3]-atanlo[3];
       } if (ix < 0x3fdc0000) {    /* |x| < 0.4375 */
           if (ix < 0x3e200000) {  /* |x| < 2^-29 */
              if(really_big+x>one) return x;     /* raise inexact */
           }
           id = -1;
       } else {
       x = fd_fabs(x);
       if (ix < 0x3ff30000) {             /* |x| < 1.1875 */
           if (ix < 0x3fe60000) {  /* 7/16 <=|x|<11/16 */
              id = 0; x = (2.0*x-one)/(2.0+x); 
           } else {                /* 11/16<=|x|< 19/16 */
              id = 1; x  = (x-one)/(x+one); 
           }
       } else {
           if (ix < 0x40038000) {  /* |x| < 2.4375 */
              id = 2; x  = (x-1.5)/(one+1.5*x);
           } else {                /* 2.4375 <= |x| < 2^66 */
              id = 3; x  = -1.0/x;
           }
       }}
    /* end of argument reduction */
       z = x*x;
       w = z*z;
    /* break sum from i=0 to 10 aT[i]z**(i+1) into odd and even poly */
       s1 = z*(aT[0]+w*(aT[2]+w*(aT[4]+w*(aT[6]+w*(aT[8]+w*aT[10])))));
       s2 = w*(aT[1]+w*(aT[3]+w*(aT[5]+w*(aT[7]+w*aT[9]))));
       if (id<0) return x - x*(s1+s2);
       else {
           z = atanhi[id] - ((x*(s1+s2) - atanlo[id]) - x);
           return (hx<0)? -z:z;
       }
}

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Variable Documentation

double aT[] [static]
Initial value:
 {

  3.33333333333329318027e-01, 
 -1.99999999998764832476e-01, 
  1.42857142725034663711e-01, 
 -1.11111104054623557880e-01, 
  9.09088713343650656196e-02, 
 -7.69187620504482999495e-02, 
  6.66107313738753120669e-02, 
 -5.83357013379057348645e-02, 
  4.97687799461593236017e-02, 
 -3.65315727442169155270e-02, 
  1.62858201153657823623e-02, 
}

Definition at line 100 of file s_atan.c.

double atanhi[] [static]
Initial value:
 {

  4.63647609000806093515e-01, 
  7.85398163397448278999e-01, 
  9.82793723247329054082e-01, 
  1.57079632679489655800e+00, 
}

Definition at line 78 of file s_atan.c.

double atanlo[] [static]
Initial value:
 {

  2.26987774529616870924e-17, 
  3.06161699786838301793e-17, 
  1.39033110312309984516e-17, 
  6.12323399573676603587e-17, 
}

Definition at line 89 of file s_atan.c.

double one = 1.0 [static]

Definition at line 120 of file s_atan.c.

double really_big = 1.0e300 [static]

Definition at line 121 of file s_atan.c.