acosf.c raw

   1  /* origin: FreeBSD /usr/src/lib/msun/src/e_acosf.c */
   2  /*
   3   * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
   4   */
   5  /*
   6   * ====================================================
   7   * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   8   *
   9   * Developed at SunPro, a Sun Microsystems, Inc. business.
  10   * Permission to use, copy, modify, and distribute this
  11   * software is freely granted, provided that this notice
  12   * is preserved.
  13   * ====================================================
  14   */
  15  
  16  #include "libm.h"
  17  
  18  static const float
  19  pio2_hi = 1.5707962513e+00, /* 0x3fc90fda */
  20  pio2_lo = 7.5497894159e-08, /* 0x33a22168 */
  21  pS0 =  1.6666586697e-01,
  22  pS1 = -4.2743422091e-02,
  23  pS2 = -8.6563630030e-03,
  24  qS1 = -7.0662963390e-01;
  25  
  26  static float R(float z)
  27  {
  28  	float_t p, q;
  29  	p = z*(pS0+z*(pS1+z*pS2));
  30  	q = 1.0f+z*qS1;
  31  	return p/q;
  32  }
  33  
  34  float acosf(float x)
  35  {
  36  	float z,w,s,c,df;
  37  	uint32_t hx,ix;
  38  
  39  	GET_FLOAT_WORD(hx, x);
  40  	ix = hx & 0x7fffffff;
  41  	/* |x| >= 1 or nan */
  42  	if (ix >= 0x3f800000) {
  43  		if (ix == 0x3f800000) {
  44  			if (hx >> 31)
  45  				return 2*pio2_hi + 0x1p-120f;
  46  			return 0;
  47  		}
  48  		return 0/(x-x);
  49  	}
  50  	/* |x| < 0.5 */
  51  	if (ix < 0x3f000000) {
  52  		if (ix <= 0x32800000) /* |x| < 2**-26 */
  53  			return pio2_hi + 0x1p-120f;
  54  		return pio2_hi - (x - (pio2_lo-x*R(x*x)));
  55  	}
  56  	/* x < -0.5 */
  57  	if (hx >> 31) {
  58  		z = (1+x)*0.5f;
  59  		s = sqrtf(z);
  60  		w = R(z)*s-pio2_lo;
  61  		return 2*(pio2_hi - (s+w));
  62  	}
  63  	/* x > 0.5 */
  64  	z = (1-x)*0.5f;
  65  	s = sqrtf(z);
  66  	GET_FLOAT_WORD(hx,s);
  67  	SET_FLOAT_WORD(df,hx&0xfffff000);
  68  	c = (z-df*df)/(s+df);
  69  	w = R(z)*s+c;
  70  	return 2*(df+w);
  71  }
  72