s_atanf.c revision 8870
1/* s_atanf.c -- float version of s_atan.c. 2 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@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#ifndef lint 17static char rcsid[] = "$Id: s_atanf.c,v 1.1.1.1 1994/08/19 09:39:57 jkh Exp $"; 18#endif 19 20#include "math.h" 21#include "math_private.h" 22 23#ifdef __STDC__ 24static const float atanhi[] = { 25#else 26static float atanhi[] = { 27#endif 28 4.6364760399e-01, /* atan(0.5)hi 0x3eed6338 */ 29 7.8539812565e-01, /* atan(1.0)hi 0x3f490fda */ 30 9.8279368877e-01, /* atan(1.5)hi 0x3f7b985e */ 31 1.5707962513e+00, /* atan(inf)hi 0x3fc90fda */ 32}; 33 34#ifdef __STDC__ 35static const float atanlo[] = { 36#else 37static float atanlo[] = { 38#endif 39 5.0121582440e-09, /* atan(0.5)lo 0x31ac3769 */ 40 3.7748947079e-08, /* atan(1.0)lo 0x33222168 */ 41 3.4473217170e-08, /* atan(1.5)lo 0x33140fb4 */ 42 7.5497894159e-08, /* atan(inf)lo 0x33a22168 */ 43}; 44 45#ifdef __STDC__ 46static const float aT[] = { 47#else 48static float aT[] = { 49#endif 50 3.3333334327e-01, /* 0x3eaaaaaa */ 51 -2.0000000298e-01, /* 0xbe4ccccd */ 52 1.4285714924e-01, /* 0x3e124925 */ 53 -1.1111110449e-01, /* 0xbde38e38 */ 54 9.0908870101e-02, /* 0x3dba2e6e */ 55 -7.6918758452e-02, /* 0xbd9d8795 */ 56 6.6610731184e-02, /* 0x3d886b35 */ 57 -5.8335702866e-02, /* 0xbd6ef16b */ 58 4.9768779427e-02, /* 0x3d4bda59 */ 59 -3.6531571299e-02, /* 0xbd15a221 */ 60 1.6285819933e-02, /* 0x3c8569d7 */ 61}; 62 63#ifdef __STDC__ 64 static const float 65#else 66 static float 67#endif 68one = 1.0, 69huge = 1.0e30; 70 71#ifdef __STDC__ 72 float atanf(float x) 73#else 74 float atanf(x) 75 float x; 76#endif 77{ 78 float w,s1,s2,z; 79 int32_t ix,hx,id; 80 81 GET_FLOAT_WORD(hx,x); 82 ix = hx&0x7fffffff; 83 if(ix>=0x50800000) { /* if |x| >= 2^34 */ 84 if(ix>0x7f800000) 85 return x+x; /* NaN */ 86 if(hx>0) return atanhi[3]+atanlo[3]; 87 else return -atanhi[3]-atanlo[3]; 88 } if (ix < 0x3ee00000) { /* |x| < 0.4375 */ 89 if (ix < 0x31000000) { /* |x| < 2^-29 */ 90 if(huge+x>one) return x; /* raise inexact */ 91 } 92 id = -1; 93 } else { 94 x = fabsf(x); 95 if (ix < 0x3f980000) { /* |x| < 1.1875 */ 96 if (ix < 0x3f300000) { /* 7/16 <=|x|<11/16 */ 97 id = 0; x = ((float)2.0*x-one)/((float)2.0+x); 98 } else { /* 11/16<=|x|< 19/16 */ 99 id = 1; x = (x-one)/(x+one); 100 } 101 } else { 102 if (ix < 0x401c0000) { /* |x| < 2.4375 */ 103 id = 2; x = (x-(float)1.5)/(one+(float)1.5*x); 104 } else { /* 2.4375 <= |x| < 2^66 */ 105 id = 3; x = -(float)1.0/x; 106 } 107 }} 108 /* end of argument reduction */ 109 z = x*x; 110 w = z*z; 111 /* break sum from i=0 to 10 aT[i]z**(i+1) into odd and even poly */ 112 s1 = z*(aT[0]+w*(aT[2]+w*(aT[4]+w*(aT[6]+w*(aT[8]+w*aT[10]))))); 113 s2 = w*(aT[1]+w*(aT[3]+w*(aT[5]+w*(aT[7]+w*aT[9])))); 114 if (id<0) return x - x*(s1+s2); 115 else { 116 z = atanhi[id] - ((x*(s1+s2) - atanlo[id]) - x); 117 return (hx<0)? -z:z; 118 } 119} 120