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00013 #if defined(LIBM_SCCS) && !defined(lint)
00014 static char rcsid[] = "$NetBSD: s_atan.c,v 1.8 1995/05/10 20:46:45 jtc Exp $";
00015 #endif
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00037 #include "math.h"
00038 #include "mathP.h"
00039
00040 #ifdef __STDC__
00041 static const double atanhi[] = {
00042 #else
00043 static double atanhi[] = {
00044 #endif
00045 4.63647609000806093515e-01,
00046 7.85398163397448278999e-01,
00047 9.82793723247329054082e-01,
00048 1.57079632679489655800e+00,
00049 };
00050
00051 #ifdef __STDC__
00052 static const double atanlo[] = {
00053 #else
00054 static double atanlo[] = {
00055 #endif
00056 2.26987774529616870924e-17,
00057 3.06161699786838301793e-17,
00058 1.39033110312309984516e-17,
00059 6.12323399573676603587e-17,
00060 };
00061
00062 #ifdef __STDC__
00063 static const double aT[] = {
00064 #else
00065 static double aT[] = {
00066 #endif
00067 3.33333333333329318027e-01,
00068 -1.99999999998764832476e-01,
00069 1.42857142725034663711e-01,
00070 -1.11111104054623557880e-01,
00071 9.09088713343650656196e-02,
00072 -7.69187620504482999495e-02,
00073 6.66107313738753120669e-02,
00074 -5.83357013379057348645e-02,
00075 4.97687799461593236017e-02,
00076 -3.65315727442169155270e-02,
00077 1.62858201153657823623e-02,
00078 };
00079
00080 #ifdef __STDC__
00081 static const double
00082 #else
00083 static double
00084 #endif
00085 one = 1.0,
00086 huge = 1.0e300;
00087
00088 #ifdef __STDC__
00089 double atan(double x)
00090 #else
00091 double atan(x)
00092 double x;
00093 #endif
00094 {
00095 double w,s1,s2,z;
00096 int32_t ix,hx,id;
00097
00098 GET_HIGH_WORD(hx,x);
00099 ix = hx&0x7fffffff;
00100 if(ix>=0x44100000) {
00101 u_int32_t low;
00102 GET_LOW_WORD(low,x);
00103 if(ix>0x7ff00000||
00104 (ix==0x7ff00000&&(low!=0)))
00105 return x+x;
00106 if(hx>0) return atanhi[3]+atanlo[3];
00107 else return -atanhi[3]-atanlo[3];
00108 } if (ix < 0x3fdc0000) {
00109 if (ix < 0x3e200000) {
00110 if(huge+x>one) return x;
00111 }
00112 id = -1;
00113 } else {
00114 x = fabs(x);
00115 if (ix < 0x3ff30000) {
00116 if (ix < 0x3fe60000) {
00117 id = 0; x = (2.0*x-one)/(2.0+x);
00118 } else {
00119 id = 1; x = (x-one)/(x+one);
00120 }
00121 } else {
00122 if (ix < 0x40038000) {
00123 id = 2; x = (x-1.5)/(one+1.5*x);
00124 } else {
00125 id = 3; x = -1.0/x;
00126 }
00127 }}
00128
00129 z = x*x;
00130 w = z*z;
00131
00132 s1 = z*(aT[0]+w*(aT[2]+w*(aT[4]+w*(aT[6]+w*(aT[8]+w*aT[10])))));
00133 s2 = w*(aT[1]+w*(aT[3]+w*(aT[5]+w*(aT[7]+w*aT[9]))));
00134 if (id<0) return x - x*(s1+s2);
00135 else {
00136 z = atanhi[id] - ((x*(s1+s2) - atanlo[id]) - x);
00137 return (hx<0)? -z:z;
00138 }
00139 }