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 #include "math.h" 17 #include "math_private.h" 18 19 static const float atanhi[] = { 20 4.6364760399e-01, /* atan(0.5)hi 0x3eed6338 */ 21 7.8539812565e-01, /* atan(1.0)hi 0x3f490fda */ 22 9.8279368877e-01, /* atan(1.5)hi 0x3f7b985e */ 23 1.5707962513e+00, /* atan(inf)hi 0x3fc90fda */ 24 }; 25 26 static const float atanlo[] = { 27 5.0121582440e-09, /* atan(0.5)lo 0x31ac3769 */ 28 3.7748947079e-08, /* atan(1.0)lo 0x33222168 */ 29 3.4473217170e-08, /* atan(1.5)lo 0x33140fb4 */ 30 7.5497894159e-08, /* atan(inf)lo 0x33a22168 */ 31 }; 32 33 static const float aT[] = { 34 3.3333328366e-01, 35 -1.9999158382e-01, 36 1.4253635705e-01, 37 -1.0648017377e-01, 38 6.1687607318e-02, 39 }; 40 41 static const float 42 one = 1.0, 43 huge = 1.0e30; 44 45 float 46 atanf(float x) 47 { 48 float w,s1,s2,z; 49 int32_t ix,hx,id; 50 51 GET_FLOAT_WORD(hx,x); 52 ix = hx&0x7fffffff; 53 if(ix>=0x4c800000) { /* if |x| >= 2**26 */ 54 if(ix>0x7f800000) 55 return x+x; /* NaN */ 56 if(hx>0) return atanhi[3]+*(volatile float *)&atanlo[3]; 57 else return -atanhi[3]-*(volatile float *)&atanlo[3]; 58 } if (ix < 0x3ee00000) { /* |x| < 0.4375 */ 59 if (ix < 0x39800000) { /* |x| < 2**-12 */ 60 if(huge+x>one) return x; /* raise inexact */ 61 } 62 id = -1; 63 } else { 64 x = fabsf(x); 65 if (ix < 0x3f980000) { /* |x| < 1.1875 */ 66 if (ix < 0x3f300000) { /* 7/16 <=|x|<11/16 */ 67 id = 0; x = ((float)2.0*x-one)/((float)2.0+x); 68 } else { /* 11/16<=|x|< 19/16 */ 69 id = 1; x = (x-one)/(x+one); 70 } 71 } else { 72 if (ix < 0x401c0000) { /* |x| < 2.4375 */ 73 id = 2; x = (x-(float)1.5)/(one+(float)1.5*x); 74 } else { /* 2.4375 <= |x| < 2**26 */ 75 id = 3; x = -(float)1.0/x; 76 } 77 }} 78 /* end of argument reduction */ 79 z = x*x; 80 w = z*z; 81 /* break sum from i=0 to 10 aT[i]z**(i+1) into odd and even poly */ 82 s1 = z*(aT[0]+w*(aT[2]+w*aT[4])); 83 s2 = w*(aT[1]+w*aT[3]); 84 if (id<0) return x - x*(s1+s2); 85 else { 86 z = atanhi[id] - ((x*(s1+s2) - atanlo[id]) - x); 87 return (hx<0)? -z:z; 88 } 89 } 90