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glibc  2.9
e_acosf.c
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00001 /* e_acosf.c -- float version of e_acos.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: e_acosf.c,v 1.5 1995/05/12 04:57:16 jtc Exp $";
00018 #endif
00019 
00020 #include "math.h"
00021 #include "math_private.h"
00022 
00023 #ifdef __STDC__
00024 static const float 
00025 #else
00026 static float 
00027 #endif
00028 one =  1.0000000000e+00, /* 0x3F800000 */
00029 pi =  3.1415925026e+00, /* 0x40490fda */
00030 pio2_hi =  1.5707962513e+00, /* 0x3fc90fda */
00031 pio2_lo =  7.5497894159e-08, /* 0x33a22168 */
00032 pS0 =  1.6666667163e-01, /* 0x3e2aaaab */
00033 pS1 = -3.2556581497e-01, /* 0xbea6b090 */
00034 pS2 =  2.0121252537e-01, /* 0x3e4e0aa8 */
00035 pS3 = -4.0055535734e-02, /* 0xbd241146 */
00036 pS4 =  7.9153501429e-04, /* 0x3a4f7f04 */
00037 pS5 =  3.4793309169e-05, /* 0x3811ef08 */
00038 qS1 = -2.4033949375e+00, /* 0xc019d139 */
00039 qS2 =  2.0209457874e+00, /* 0x4001572d */
00040 qS3 = -6.8828397989e-01, /* 0xbf303361 */
00041 qS4 =  7.7038154006e-02; /* 0x3d9dc62e */
00042 
00043 #ifdef __STDC__
00044        float __ieee754_acosf(float x)
00045 #else
00046        float __ieee754_acosf(x)
00047        float x;
00048 #endif
00049 {
00050        float z,p,q,r,w,s,c,df;
00051        int32_t hx,ix;
00052        GET_FLOAT_WORD(hx,x);
00053        ix = hx&0x7fffffff;
00054        if(ix==0x3f800000) {        /* |x|==1 */
00055            if(hx>0) return 0.0;    /* acos(1) = 0  */
00056            else return pi+(float)2.0*pio2_lo;    /* acos(-1)= pi */
00057        } else if(ix>0x3f800000) {  /* |x| >= 1 */
00058            return (x-x)/(x-x);            /* acos(|x|>1) is NaN */
00059        }
00060        if(ix<0x3f000000) {  /* |x| < 0.5 */
00061            if(ix<=0x23000000) return pio2_hi+pio2_lo;/*if|x|<2**-57*/
00062            z = x*x;
00063            p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
00064            q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
00065            r = p/q;
00066            return pio2_hi - (x - (pio2_lo-x*r));
00067        } else  if (hx<0) {         /* x < -0.5 */
00068            z = (one+x)*(float)0.5;
00069            p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
00070            q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
00071            s = __ieee754_sqrtf(z);
00072            r = p/q;
00073            w = r*s-pio2_lo;
00074            return pi - (float)2.0*(s+w);
00075        } else {                    /* x > 0.5 */
00076            int32_t idf;
00077            z = (one-x)*(float)0.5;
00078            s = __ieee754_sqrtf(z);
00079            df = s;
00080            GET_FLOAT_WORD(idf,df);
00081            SET_FLOAT_WORD(df,idf&0xfffff000);
00082            c  = (z-df*df)/(s+df);
00083            p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
00084            q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
00085            r = p/q;
00086            w = r*s+c;
00087            return (float)2.0*(df+w);
00088        }
00089 }