nsz Git - musl/blob - 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 pi      = 3.1415925026e+00, /* 0x40490fda */
  20 pio2_hi = 1.5707962513e+00; /* 0x3fc90fda */
  21 static const volatile float
  22 pio2_lo = 7.5497894159e-08; /* 0x33a22168 */
  23 static const float
  24 pS0 =  1.6666586697e-01,
  25 pS1 = -4.2743422091e-02,
  26 pS2 = -8.6563630030e-03,
  27 qS1 = -7.0662963390e-01;
  28
  29 float acosf(float x)
  30 {
  31         float z,p,q,r,w,s,c,df;
  32         int32_t hx,ix;
  33
  34         GET_FLOAT_WORD(hx, x);
  35         ix = hx & 0x7fffffff;
  36         if (ix >= 0x3f800000) {  /* |x| >= 1 */
  37                 if (ix == 0x3f800000) {  /* |x| == 1 */
  38                         if (hx > 0) return 0.0f;  /* acos(1) = 0 */
  39                         return pi + 2.0f*pio2_lo;  /* acos(-1)= pi */
  40                 }
  41                 return (x-x)/(x-x);  /* acos(|x|>1) is NaN */
  42         }
  43         if (ix < 0x3f000000) {   /* |x| < 0.5 */
  44                 if (ix <= 0x32800000) /* |x| < 2**-26 */
  45                         return pio2_hi + pio2_lo;
  46                 z = x*x;
  47                 p = z*(pS0+z*(pS1+z*pS2));
  48                 q = 1.0f+z*qS1;
  49                 r = p/q;
  50                 return pio2_hi - (x - (pio2_lo-x*r));
  51         } else if (hx < 0) {     /* x < -0.5 */
  52                 z = (1.0f+x)*0.5f;
  53                 p = z*(pS0+z*(pS1+z*pS2));
  54                 q = 1.0f+z*qS1;
  55                 s = sqrtf(z);
  56                 r = p/q;
  57                 w = r*s-pio2_lo;
  58                 return pi - 2.0f*(s+w);
  59         } else {                 /* x > 0.5 */
  60                 int32_t idf;
  61
  62                 z = (1.0f-x)*0.5f;
  63                 s = sqrtf(z);
  64                 df = s;
  65                 GET_FLOAT_WORD(idf,df);
  66                 SET_FLOAT_WORD(df,idf&0xfffff000);
  67                 c  = (z-df*df)/(s+df);
  68                 p = z*(pS0+z*(pS1+z*pS2));
  69                 q = 1.0f+z*qS1;
  70                 r = p/q;
  71                 w = r*s+c;
  72                 return 2.0f*(df+w);
  73         }
  74 }