| The Android Open Source Project | 1dc9e47 | 2009-03-03 19:28:35 -0800 | [diff] [blame] | 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 |
| 17 | static char rcsid[] = "$FreeBSD: src/lib/msun/src/s_atanf.c,v 1.7 2002/05/28 18:15:04 alfred Exp $"; |
| 18 | #endif |
| 19 | |
| 20 | #include "math.h" |
| 21 | #include "math_private.h" |
| 22 | |
| 23 | static const float atanhi[] = { |
| 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 | static const float atanlo[] = { |
| 31 | 5.0121582440e-09, /* atan(0.5)lo 0x31ac3769 */ |
| 32 | 3.7748947079e-08, /* atan(1.0)lo 0x33222168 */ |
| 33 | 3.4473217170e-08, /* atan(1.5)lo 0x33140fb4 */ |
| 34 | 7.5497894159e-08, /* atan(inf)lo 0x33a22168 */ |
| 35 | }; |
| 36 | |
| 37 | static const float aT[] = { |
| 38 | 3.3333334327e-01, /* 0x3eaaaaaa */ |
| 39 | -2.0000000298e-01, /* 0xbe4ccccd */ |
| 40 | 1.4285714924e-01, /* 0x3e124925 */ |
| 41 | -1.1111110449e-01, /* 0xbde38e38 */ |
| 42 | 9.0908870101e-02, /* 0x3dba2e6e */ |
| 43 | -7.6918758452e-02, /* 0xbd9d8795 */ |
| 44 | 6.6610731184e-02, /* 0x3d886b35 */ |
| 45 | -5.8335702866e-02, /* 0xbd6ef16b */ |
| 46 | 4.9768779427e-02, /* 0x3d4bda59 */ |
| 47 | -3.6531571299e-02, /* 0xbd15a221 */ |
| 48 | 1.6285819933e-02, /* 0x3c8569d7 */ |
| 49 | }; |
| 50 | |
| 51 | static const float |
| 52 | one = 1.0, |
| 53 | huge = 1.0e30; |
| 54 | |
| 55 | float |
| 56 | atanf(float x) |
| 57 | { |
| 58 | float w,s1,s2,z; |
| 59 | int32_t ix,hx,id; |
| 60 | |
| 61 | GET_FLOAT_WORD(hx,x); |
| 62 | ix = hx&0x7fffffff; |
| 63 | if(ix>=0x50800000) { /* if |x| >= 2^34 */ |
| 64 | if(ix>0x7f800000) |
| 65 | return x+x; /* NaN */ |
| 66 | if(hx>0) return atanhi[3]+atanlo[3]; |
| 67 | else return -atanhi[3]-atanlo[3]; |
| 68 | } if (ix < 0x3ee00000) { /* |x| < 0.4375 */ |
| 69 | if (ix < 0x31000000) { /* |x| < 2^-29 */ |
| 70 | if(huge+x>one) return x; /* raise inexact */ |
| 71 | } |
| 72 | id = -1; |
| 73 | } else { |
| 74 | x = fabsf(x); |
| 75 | if (ix < 0x3f980000) { /* |x| < 1.1875 */ |
| 76 | if (ix < 0x3f300000) { /* 7/16 <=|x|<11/16 */ |
| 77 | id = 0; x = ((float)2.0*x-one)/((float)2.0+x); |
| 78 | } else { /* 11/16<=|x|< 19/16 */ |
| 79 | id = 1; x = (x-one)/(x+one); |
| 80 | } |
| 81 | } else { |
| 82 | if (ix < 0x401c0000) { /* |x| < 2.4375 */ |
| 83 | id = 2; x = (x-(float)1.5)/(one+(float)1.5*x); |
| 84 | } else { /* 2.4375 <= |x| < 2^66 */ |
| 85 | id = 3; x = -(float)1.0/x; |
| 86 | } |
| 87 | }} |
| 88 | /* end of argument reduction */ |
| 89 | z = x*x; |
| 90 | w = z*z; |
| 91 | /* break sum from i=0 to 10 aT[i]z**(i+1) into odd and even poly */ |
| 92 | s1 = z*(aT[0]+w*(aT[2]+w*(aT[4]+w*(aT[6]+w*(aT[8]+w*aT[10]))))); |
| 93 | s2 = w*(aT[1]+w*(aT[3]+w*(aT[5]+w*(aT[7]+w*aT[9])))); |
| 94 | if (id<0) return x - x*(s1+s2); |
| 95 | else { |
| 96 | z = atanhi[id] - ((x*(s1+s2) - atanlo[id]) - x); |
| 97 | return (hx<0)? -z:z; |
| 98 | } |
| 99 | } |