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      1 /* sf_atan.c -- float version of s_atan.c.
      2  * Conversion to float by Ian Lance Taylor, Cygnus Support, ian (at) cygnus.com.
      3  */
      4 
      5 /*
      6  * ====================================================
      7  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
      8  *
      9  * Developed at SunPro, a Sun Microsystems, Inc. business.
     10  * Permission to use, copy, modify, and distribute this
     11  * software is freely granted, provided that this notice
     12  * is preserved.
     13  * ====================================================
     14  *
     15  */
     16 
     17 #include "fdlibm.h"
     18 
     19 #ifdef __STDC__
     20 static const float atanhi[] = {
     21 #else
     22 static float atanhi[] = {
     23 #endif
     24   4.6364760399e-01, /* atan(0.5)hi 0x3eed6338 */
     25   7.8539812565e-01, /* atan(1.0)hi 0x3f490fda */
     26   9.8279368877e-01, /* atan(1.5)hi 0x3f7b985e */
     27   1.5707962513e+00, /* atan(inf)hi 0x3fc90fda */
     28 };
     29 
     30 #ifdef __STDC__
     31 static const float atanlo[] = {
     32 #else
     33 static float atanlo[] = {
     34 #endif
     35   5.0121582440e-09, /* atan(0.5)lo 0x31ac3769 */
     36   3.7748947079e-08, /* atan(1.0)lo 0x33222168 */
     37   3.4473217170e-08, /* atan(1.5)lo 0x33140fb4 */
     38   7.5497894159e-08, /* atan(inf)lo 0x33a22168 */
     39 };
     40 
     41 #ifdef __STDC__
     42 static const float aT[] = {
     43 #else
     44 static float aT[] = {
     45 #endif
     46   3.3333334327e-01, /* 0x3eaaaaaa */
     47  -2.0000000298e-01, /* 0xbe4ccccd */
     48   1.4285714924e-01, /* 0x3e124925 */
     49  -1.1111110449e-01, /* 0xbde38e38 */
     50   9.0908870101e-02, /* 0x3dba2e6e */
     51  -7.6918758452e-02, /* 0xbd9d8795 */
     52   6.6610731184e-02, /* 0x3d886b35 */
     53  -5.8335702866e-02, /* 0xbd6ef16b */
     54   4.9768779427e-02, /* 0x3d4bda59 */
     55  -3.6531571299e-02, /* 0xbd15a221 */
     56   1.6285819933e-02, /* 0x3c8569d7 */
     57 };
     58 
     59 #ifdef __STDC__
     60 	static const float
     61 #else
     62 	static float
     63 #endif
     64 one   = 1.0,
     65 huge   = 1.0e30;
     66 
     67 #ifdef __STDC__
     68 	float atanf(float x)
     69 #else
     70 	float atanf(x)
     71 	float x;
     72 #endif
     73 {
     74 	float w,s1,s2,z;
     75 	__int32_t ix,hx,id;
     76 
     77 	GET_FLOAT_WORD(hx,x);
     78 	ix = hx&0x7fffffff;
     79 	if(ix>=0x50800000) {	/* if |x| >= 2^34 */
     80 	    if(FLT_UWORD_IS_NAN(ix))
     81 		return x+x;		/* NaN */
     82 	    if(hx>0) return  atanhi[3]+atanlo[3];
     83 	    else     return -atanhi[3]-atanlo[3];
     84 	} if (ix < 0x3ee00000) {	/* |x| < 0.4375 */
     85 	    if (ix < 0x31000000) {	/* |x| < 2^-29 */
     86 		if(huge+x>one) return x;	/* raise inexact */
     87 	    }
     88 	    id = -1;
     89 	} else {
     90 	x = fabsf(x);
     91 	if (ix < 0x3f980000) {		/* |x| < 1.1875 */
     92 	    if (ix < 0x3f300000) {	/* 7/16 <=|x|<11/16 */
     93 		id = 0; x = ((float)2.0*x-one)/((float)2.0+x);
     94 	    } else {			/* 11/16<=|x|< 19/16 */
     95 		id = 1; x  = (x-one)/(x+one);
     96 	    }
     97 	} else {
     98 	    if (ix < 0x401c0000) {	/* |x| < 2.4375 */
     99 		id = 2; x  = (x-(float)1.5)/(one+(float)1.5*x);
    100 	    } else {			/* 2.4375 <= |x| < 2^66 */
    101 		id = 3; x  = -(float)1.0/x;
    102 	    }
    103 	}}
    104     /* end of argument reduction */
    105 	z = x*x;
    106 	w = z*z;
    107     /* break sum from i=0 to 10 aT[i]z**(i+1) into odd and even poly */
    108 	s1 = z*(aT[0]+w*(aT[2]+w*(aT[4]+w*(aT[6]+w*(aT[8]+w*aT[10])))));
    109 	s2 = w*(aT[1]+w*(aT[3]+w*(aT[5]+w*(aT[7]+w*aT[9]))));
    110 	if (id<0) return x - x*(s1+s2);
    111 	else {
    112 	    z = atanhi[id] - ((x*(s1+s2) - atanlo[id]) - x);
    113 	    return (hx<0)? -z:z;
    114 	}
    115 }
    116 
    117 #ifdef _DOUBLE_IS_32BITS
    118 
    119 #ifdef __STDC__
    120 	double atan(double x)
    121 #else
    122 	double atan(x)
    123 	double x;
    124 #endif
    125 {
    126 	return (double) atanf((float) x);
    127 }
    128 
    129 #endif /* defined(_DOUBLE_IS_32BITS) */
    130