asinf.c raw

   1  /* origin: FreeBSD /usr/src/lib/msun/src/e_asinf.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  #include "libm.h"
  16  
  17  static const double
  18  pio2 = 1.570796326794896558e+00;
  19  
  20  static const float
  21  /* coefficients for R(x^2) */
  22  pS0 =  1.6666586697e-01,
  23  pS1 = -4.2743422091e-02,
  24  pS2 = -8.6563630030e-03,
  25  qS1 = -7.0662963390e-01;
  26  
  27  static float R(float z)
  28  {
  29  	float_t p, q;
  30  	p = z*(pS0+z*(pS1+z*pS2));
  31  	q = 1.0f+z*qS1;
  32  	return p/q;
  33  }
  34  
  35  float asinf(float x)
  36  {
  37  	double s;
  38  	float z;
  39  	uint32_t hx,ix;
  40  
  41  	GET_FLOAT_WORD(hx, x);
  42  	ix = hx & 0x7fffffff;
  43  	if (ix >= 0x3f800000) {  /* |x| >= 1 */
  44  		if (ix == 0x3f800000)  /* |x| == 1 */
  45  			return x*pio2 + 0x1p-120f;  /* asin(+-1) = +-pi/2 with inexact */
  46  		return 0/(x-x);  /* asin(|x|>1) is NaN */
  47  	}
  48  	if (ix < 0x3f000000) {  /* |x| < 0.5 */
  49  		/* if 0x1p-126 <= |x| < 0x1p-12, avoid raising underflow */
  50  		if (ix < 0x39800000 && ix >= 0x00800000)
  51  			return x;
  52  		return x + x*R(x*x);
  53  	}
  54  	/* 1 > |x| >= 0.5 */
  55  	z = (1 - fabsf(x))*0.5f;
  56  	s = sqrt(z);
  57  	x = pio2 - 2*(s+s*R(z));
  58  	if (hx >> 31)
  59  		return -x;
  60  	return x;
  61  }
  62