POK
/home/jaouen/pok_official/pok/trunk/libpok/libm/e_acosf.c
00001 /*
00002  *                               POK header
00003  * 
00004  * The following file is a part of the POK project. Any modification should
00005  * made according to the POK licence. You CANNOT use this file or a part of
00006  * this file is this part of a file for your own project
00007  *
00008  * For more information on the POK licence, please see our LICENCE FILE
00009  *
00010  * Please follow the coding guidelines described in doc/CODING_GUIDELINES
00011  *
00012  *                                      Copyright (c) 2007-2009 POK team 
00013  *
00014  * Created by julien on Fri Jan 30 14:41:34 2009 
00015  */
00016 
00017 /* e_acosf.c -- float version of e_acos.c.
00018  * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
00019  */
00020 
00021 /*
00022  * ====================================================
00023  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
00024  *
00025  * Developed at SunPro, a Sun Microsystems, Inc. business.
00026  * Permission to use, copy, modify, and distribute this
00027  * software is freely granted, provided that this notice
00028  * is preserved.
00029  * ====================================================
00030  */
00031 
00032 #ifdef POK_NEEDS_LIBMATH
00033 
00034 #include "math_private.h"
00035 
00036 static const float
00037 one =  1.0000000000e+00, /* 0x3F800000 */
00038 pi =  3.1415925026e+00, /* 0x40490fda */
00039 pio2_hi =  1.5707962513e+00, /* 0x3fc90fda */
00040 pio2_lo =  7.5497894159e-08, /* 0x33a22168 */
00041 pS0 =  1.6666667163e-01, /* 0x3e2aaaab */
00042 pS1 = -3.2556581497e-01, /* 0xbea6b090 */
00043 pS2 =  2.0121252537e-01, /* 0x3e4e0aa8 */
00044 pS3 = -4.0055535734e-02, /* 0xbd241146 */
00045 pS4 =  7.9153501429e-04, /* 0x3a4f7f04 */
00046 pS5 =  3.4793309169e-05, /* 0x3811ef08 */
00047 qS1 = -2.4033949375e+00, /* 0xc019d139 */
00048 qS2 =  2.0209457874e+00, /* 0x4001572d */
00049 qS3 = -6.8828397989e-01, /* 0xbf303361 */
00050 qS4 =  7.7038154006e-02; /* 0x3d9dc62e */
00051 
00052 float
00053 __ieee754_acosf(float x)
00054 {
00055         float z,p,q,r,w,s,c,df;
00056         int32_t hx,ix;
00057         GET_FLOAT_WORD(hx,x);
00058         ix = hx&0x7fffffff;
00059         if(ix==0x3f800000) {            /* |x|==1 */
00060             if(hx>0) return 0.0;        /* acos(1) = 0  */
00061             else return pi+(float)2.0*pio2_lo;  /* acos(-1)= pi */
00062         } else if(ix>0x3f800000) {      /* |x| >= 1 */
00063             return (x-x)/(x-x);         /* acos(|x|>1) is NaN */
00064         }
00065         if(ix<0x3f000000) {     /* |x| < 0.5 */
00066             if(ix<=0x23000000) return pio2_hi+pio2_lo;/*if|x|<2**-57*/
00067             z = x*x;
00068             p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
00069             q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
00070             r = p/q;
00071             return pio2_hi - (x - (pio2_lo-x*r));
00072         } else  if (hx<0) {             /* x < -0.5 */
00073             z = (one+x)*(float)0.5;
00074             p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
00075             q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
00076             s = __ieee754_sqrtf(z);
00077             r = p/q;
00078             w = r*s-pio2_lo;
00079             return pi - (float)2.0*(s+w);
00080         } else {                        /* x > 0.5 */
00081             int32_t idf;
00082             z = (one-x)*(float)0.5;
00083             s = __ieee754_sqrtf(z);
00084             df = s;
00085             GET_FLOAT_WORD(idf,df);
00086             SET_FLOAT_WORD(df,idf&0xfffff000);
00087             c  = (z-df*df)/(s+df);
00088             p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
00089             q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
00090             r = p/q;
00091             w = r*s+c;
00092             return (float)2.0*(df+w);
00093         }
00094 }
00095 #endif
00096