src/math/acosf.c

   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 }