1  /* e_acosf.c -- float version of e_acos.c.
       2   */
       3  
       4  /*
       5   * ====================================================
       6   * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
       7   *
       8   * Developed at SunPro, a Sun Microsystems, Inc. business.
       9   * Permission to use, copy, modify, and distribute this
      10   * software is freely granted, provided that this notice
      11   * is preserved.
      12   * ====================================================
      13   */
      14  
      15  #include <math.h>
      16  #include <math_private.h>
      17  #include <libm-alias-finite.h>
      18  
      19  static const float
      20  one =  1.0000000000e+00, /* 0x3F800000 */
      21  pi =  3.1415925026e+00, /* 0x40490fda */
      22  pio2_hi =  1.5707962513e+00, /* 0x3fc90fda */
      23  pio2_lo =  7.5497894159e-08, /* 0x33a22168 */
      24  pS0 =  1.6666667163e-01, /* 0x3e2aaaab */
      25  pS1 = -3.2556581497e-01, /* 0xbea6b090 */
      26  pS2 =  2.0121252537e-01, /* 0x3e4e0aa8 */
      27  pS3 = -4.0055535734e-02, /* 0xbd241146 */
      28  pS4 =  7.9153501429e-04, /* 0x3a4f7f04 */
      29  pS5 =  3.4793309169e-05, /* 0x3811ef08 */
      30  qS1 = -2.4033949375e+00, /* 0xc019d139 */
      31  qS2 =  2.0209457874e+00, /* 0x4001572d */
      32  qS3 = -6.8828397989e-01, /* 0xbf303361 */
      33  qS4 =  7.7038154006e-02; /* 0x3d9dc62e */
      34  
      35  float
      36  __ieee754_acosf(float x)
      37  {
      38  	float z,p,q,r,w,s,c,df;
      39  	int32_t hx,ix;
      40  	GET_FLOAT_WORD(hx,x);
      41  	ix = hx&0x7fffffff;
      42  	if(ix==0x3f800000) {		/* |x|==1 */
      43  	    if(hx>0) return 0.0;	/* acos(1) = 0  */
      44  	    else return pi+(float)2.0*pio2_lo;	/* acos(-1)= pi */
      45  	} else if(ix>0x3f800000) {	/* |x| >= 1 */
      46  	    return (x-x)/(x-x);		/* acos(|x|>1) is NaN */
      47  	}
      48  	if(ix<0x3f000000) {	/* |x| < 0.5 */
      49  	    if(ix<=0x32800000) return pio2_hi+pio2_lo;/*if|x|<=2**-26*/
      50  	    z = x*x;
      51  	    p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
      52  	    q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
      53  	    r = p/q;
      54  	    return pio2_hi - (x - (pio2_lo-x*r));
      55  	} else  if (hx<0) {		/* x < -0.5 */
      56  	    z = (one+x)*(float)0.5;
      57  	    p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
      58  	    q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
      59  	    s = sqrtf(z);
      60  	    r = p/q;
      61  	    w = r*s-pio2_lo;
      62  	    return pi - (float)2.0*(s+w);
      63  	} else {			/* x > 0.5 */
      64  	    int32_t idf;
      65  	    z = (one-x)*(float)0.5;
      66  	    s = sqrtf(z);
      67  	    df = s;
      68  	    GET_FLOAT_WORD(idf,df);
      69  	    SET_FLOAT_WORD(df,idf&0xfffff000);
      70  	    c  = (z-df*df)/(s+df);
      71  	    p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
      72  	    q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
      73  	    r = p/q;
      74  	    w = r*s+c;
      75  	    return (float)2.0*(df+w);
      76  	}
      77  }
      78  libm_alias_finite (__ieee754_acosf, __acosf)