1 /* origin: FreeBSD /usr/src/lib/msun/src/s_atanf.c */ 2 /* 3 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com. 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 "libm.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 float atanf(float x) 42 { 43 float_t w,s1,s2,z; 44 uint32_t ix,sign; 45 int id; 46 47 GET_FLOAT_WORD(ix, x); 48 sign = ix>>31; 49 ix &= 0x7fffffff; 50 if (ix >= 0x4c800000) { /* if |x| >= 2**26 */ 51 if (isnan(x)) 52 return x; 53 z = atanhi[3] + 0x1p-120f; 54 return sign ? -z : z; 55 } 56 if (ix < 0x3ee00000) { /* |x| < 0.4375 */ 57 if (ix < 0x39800000) { /* |x| < 2**-12 */ 58 if (ix < 0x00800000) 59 /* raise underflow for subnormal x */ 60 FORCE_EVAL(x*x); 61 return x; 62 } 63 id = -1; 64 } else { 65 x = fabsf(x); 66 if (ix < 0x3f980000) { /* |x| < 1.1875 */ 67 if (ix < 0x3f300000) { /* 7/16 <= |x| < 11/16 */ 68 id = 0; 69 x = (2.0f*x - 1.0f)/(2.0f + x); 70 } else { /* 11/16 <= |x| < 19/16 */ 71 id = 1; 72 x = (x - 1.0f)/(x + 1.0f); 73 } 74 } else { 75 if (ix < 0x401c0000) { /* |x| < 2.4375 */ 76 id = 2; 77 x = (x - 1.5f)/(1.0f + 1.5f*x); 78 } else { /* 2.4375 <= |x| < 2**26 */ 79 id = 3; 80 x = -1.0f/x; 81 } 82 } 83 } 84 /* end of argument reduction */ 85 z = x*x; 86 w = z*z; 87 /* break sum from i=0 to 10 aT[i]z**(i+1) into odd and even poly */ 88 s1 = z*(aT[0]+w*(aT[2]+w*aT[4])); 89 s2 = w*(aT[1]+w*aT[3]); 90 if (id < 0) 91 return x - x*(s1+s2); 92 z = atanhi[id] - ((x*(s1+s2) - atanlo[id]) - x); 93 return sign ? -z : z; 94 } 95