src/math/asinf.c

   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 }