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glibc  2.9
s_atanf.c
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00001 /* s_atanf.c -- float version of s_atan.c.
00002  * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
00003  */
00004 
00005 /*
00006  * ====================================================
00007  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
00008  *
00009  * Developed at SunPro, a Sun Microsystems, Inc. business.
00010  * Permission to use, copy, modify, and distribute this
00011  * software is freely granted, provided that this notice 
00012  * is preserved.
00013  * ====================================================
00014  */
00015 
00016 #if defined(LIBM_SCCS) && !defined(lint)
00017 static char rcsid[] = "$NetBSD: s_atanf.c,v 1.4 1995/05/10 20:46:47 jtc Exp $";
00018 #endif
00019 
00020 #include "math.h"
00021 #include "math_private.h"
00022 
00023 #ifdef __STDC__
00024 static const float atanhi[] = {
00025 #else
00026 static float atanhi[] = {
00027 #endif
00028   4.6364760399e-01, /* atan(0.5)hi 0x3eed6338 */
00029   7.8539812565e-01, /* atan(1.0)hi 0x3f490fda */
00030   9.8279368877e-01, /* atan(1.5)hi 0x3f7b985e */
00031   1.5707962513e+00, /* atan(inf)hi 0x3fc90fda */
00032 };
00033 
00034 #ifdef __STDC__
00035 static const float atanlo[] = {
00036 #else
00037 static float atanlo[] = {
00038 #endif
00039   5.0121582440e-09, /* atan(0.5)lo 0x31ac3769 */
00040   3.7748947079e-08, /* atan(1.0)lo 0x33222168 */
00041   3.4473217170e-08, /* atan(1.5)lo 0x33140fb4 */
00042   7.5497894159e-08, /* atan(inf)lo 0x33a22168 */
00043 };
00044 
00045 #ifdef __STDC__
00046 static const float aT[] = {
00047 #else
00048 static float aT[] = {
00049 #endif
00050   3.3333334327e-01, /* 0x3eaaaaaa */
00051  -2.0000000298e-01, /* 0xbe4ccccd */
00052   1.4285714924e-01, /* 0x3e124925 */
00053  -1.1111110449e-01, /* 0xbde38e38 */
00054   9.0908870101e-02, /* 0x3dba2e6e */
00055  -7.6918758452e-02, /* 0xbd9d8795 */
00056   6.6610731184e-02, /* 0x3d886b35 */
00057  -5.8335702866e-02, /* 0xbd6ef16b */
00058   4.9768779427e-02, /* 0x3d4bda59 */
00059  -3.6531571299e-02, /* 0xbd15a221 */
00060   1.6285819933e-02, /* 0x3c8569d7 */
00061 };
00062 
00063 #ifdef __STDC__
00064        static const float 
00065 #else
00066        static float 
00067 #endif
00068 one   = 1.0,
00069 huge   = 1.0e30;
00070 
00071 #ifdef __STDC__
00072        float __atanf(float x)
00073 #else
00074        float __atanf(x)
00075        float x;
00076 #endif
00077 {
00078        float w,s1,s2,z;
00079        int32_t ix,hx,id;
00080 
00081        GET_FLOAT_WORD(hx,x);
00082        ix = hx&0x7fffffff;
00083        if(ix>=0x50800000) { /* if |x| >= 2^34 */
00084            if(ix>0x7f800000)
00085               return x+x;          /* NaN */
00086            if(hx>0) return  atanhi[3]+atanlo[3];
00087            else     return -atanhi[3]-atanlo[3];
00088        } if (ix < 0x3ee00000) {    /* |x| < 0.4375 */
00089            if (ix < 0x31000000) {  /* |x| < 2^-29 */
00090               if(huge+x>one) return x;    /* raise inexact */
00091            }
00092            id = -1;
00093        } else {
00094        x = fabsf(x);
00095        if (ix < 0x3f980000) {             /* |x| < 1.1875 */
00096            if (ix < 0x3f300000) {  /* 7/16 <=|x|<11/16 */
00097               id = 0; x = ((float)2.0*x-one)/((float)2.0+x); 
00098            } else {                /* 11/16<=|x|< 19/16 */
00099               id = 1; x  = (x-one)/(x+one); 
00100            }
00101        } else {
00102            if (ix < 0x401c0000) {  /* |x| < 2.4375 */
00103               id = 2; x  = (x-(float)1.5)/(one+(float)1.5*x);
00104            } else {                /* 2.4375 <= |x| < 2^66 */
00105               id = 3; x  = -(float)1.0/x;
00106            }
00107        }}
00108     /* end of argument reduction */
00109        z = x*x;
00110        w = z*z;
00111     /* break sum from i=0 to 10 aT[i]z**(i+1) into odd and even poly */
00112        s1 = z*(aT[0]+w*(aT[2]+w*(aT[4]+w*(aT[6]+w*(aT[8]+w*aT[10])))));
00113        s2 = w*(aT[1]+w*(aT[3]+w*(aT[5]+w*(aT[7]+w*aT[9]))));
00114        if (id<0) return x - x*(s1+s2);
00115        else {
00116            z = atanhi[id] - ((x*(s1+s2) - atanlo[id]) - x);
00117            return (hx<0)? -z:z;
00118        }
00119 }
00120 weak_alias (__atanf, atanf)