e_acosf.c

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/* e_acosf.c -- float version of e_acos.c.
 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
 */

/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunPro, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice 
 * is preserved.
 * ====================================================
 */

#include "math.h"
#include "math_private.h"

static const float 
one =  1.0000000000e+00, /* 0x3F800000 */
pi =  3.1415925026e+00, /* 0x40490fda */
pio2_hi =  1.5707962513e+00, /* 0x3fc90fda */
pio2_lo =  7.5497894159e-08, /* 0x33a22168 */
pS0 =  1.6666667163e-01, /* 0x3e2aaaab */
pS1 = -3.2556581497e-01, /* 0xbea6b090 */
pS2 =  2.0121252537e-01, /* 0x3e4e0aa8 */
pS3 = -4.0055535734e-02, /* 0xbd241146 */
pS4 =  7.9153501429e-04, /* 0x3a4f7f04 */
pS5 =  3.4793309169e-05, /* 0x3811ef08 */
qS1 = -2.4033949375e+00, /* 0xc019d139 */
qS2 =  2.0209457874e+00, /* 0x4001572d */
qS3 = -6.8828397989e-01, /* 0xbf303361 */
qS4 =  7.7038154006e-02; /* 0x3d9dc62e */

float
acosf(float x)
{
    float z,p,q,r,w,s,c,df;
    int32_t hx,ix;
    GET_FLOAT_WORD(hx,x);
    ix = hx&0x7fffffff;
    if(ix==0x3f800000) {        /* |x|==1 */
        if(hx>0) return 0.0;    /* acos(1) = 0  */
        else return pi+(float)2.0*pio2_lo;  /* acos(-1)= pi */
    } else if(ix>0x3f800000) {  /* |x| >= 1 */
        return (x-x)/(x-x);     /* acos(|x|>1) is NaN */
    }
    if(ix<0x3f000000) { /* |x| < 0.5 */
        if(ix<=0x23000000) return pio2_hi+pio2_lo;/*if|x|<2**-57*/
        z = x*x;
        p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
        q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
        r = p/q;
        return pio2_hi - (x - (pio2_lo-x*r));
    } else  if (hx<0) {     /* x < -0.5 */
        z = (one+x)*(float)0.5;
        p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
        q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
        s = sqrtf(z);
        r = p/q;
        w = r*s-pio2_lo;
        return pi - (float)2.0*(s+w);
    } else {            /* x > 0.5 */
        int32_t idf;
        z = (one-x)*(float)0.5;
        s = sqrtf(z);
        df = s;
        GET_FLOAT_WORD(idf,df);
        SET_FLOAT_WORD(df,idf&0xfffff000);
        c  = (z-df*df)/(s+df);
        p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
        q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
        r = p/q;
        w = r*s+c;
        return (float)2.0*(df+w);
    }
}