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- #include "math.h"
- #include "math_private.h"
- static const double atanhi[] = {
- 4.63647609000806093515e-01,
- 7.85398163397448278999e-01,
- 9.82793723247329054082e-01,
- 1.57079632679489655800e+00,
- };
- static const double atanlo[] = {
- 2.26987774529616870924e-17,
- 3.06161699786838301793e-17,
- 1.39033110312309984516e-17,
- 6.12323399573676603587e-17,
- };
- static const double aT[] = {
- 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,
- };
- static const double
- one = 1.0,
- huge = 1.0e300;
- double atan(double x)
- {
- double w,s1,s2,z;
- int32_t ix,hx,id;
- GET_HIGH_WORD(hx,x);
- ix = hx&0x7fffffff;
- if(ix>=0x44100000) {
- u_int32_t low;
- GET_LOW_WORD(low,x);
- if(ix>0x7ff00000||
- (ix==0x7ff00000&&(low!=0)))
- return x+x;
- if(hx>0) return atanhi[3]+atanlo[3];
- else return -atanhi[3]-atanlo[3];
- } if (ix < 0x3fdc0000) {
- if (ix < 0x3e200000) {
- if(huge+x>one) return x;
- }
- id = -1;
- } else {
- x = fabs(x);
- if (ix < 0x3ff30000) {
- if (ix < 0x3fe60000) {
- id = 0; x = (2.0*x-one)/(2.0+x);
- } else {
- id = 1; x = (x-one)/(x+one);
- }
- } else {
- if (ix < 0x40038000) {
- id = 2; x = (x-1.5)/(one+1.5*x);
- } else {
- id = 3; x = -1.0/x;
- }
- }}
-
- z = x*x;
- w = z*z;
-
- 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;
- }
- }
- libm_hidden_def(atan)
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