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 one = 1.0000000000e+00, /* 0x3F800000 */
  20 pi  = 3.1415925026e+00, /* 0x40490fda */
  21 pio2_hi = 1.5707962513e+00; /* 0x3fc90fda */
  22 static volatile float
  23 pio2_lo = 7.5497894159e-08; /* 0x33a22168 */
  24 static const float
  25 pS0 =  1.6666586697e-01,
  26 pS1 = -4.2743422091e-02,
  27 pS2 = -8.6563630030e-03,
  28 qS1 = -7.0662963390e-01;
  29
  30 float acosf(float x)
  31 {
  32         float z,p,q,r,w,s,c,df;
  33         int32_t hx,ix;
  34
  35         GET_FLOAT_WORD(hx, x);
  36         ix = hx & 0x7fffffff;
  37         if (ix >= 0x3f800000) {  /* |x| >= 1 */
  38                 if (ix == 0x3f800000) {  /* |x| == 1 */
  39                         if(hx>0) return 0.0;  /* acos(1) = 0 */
  40                         return pi + (float)2.0*pio2_lo;  /* acos(-1)= pi */
  41                 }
  42                 return (x-x)/(x-x);  /* acos(|x|>1) is NaN */
  43         }
  44         if (ix < 0x3f000000) {   /* |x| < 0.5 */
  45                 if (ix <= 0x32800000) /* |x| < 2**-26 */
  46                         return pio2_hi + pio2_lo;
  47                 z = x*x;
  48                 p = z*(pS0+z*(pS1+z*pS2));
  49                 q = one+z*qS1;
  50                 r = p/q;
  51                 return pio2_hi - (x - (pio2_lo-x*r));
  52         } else if (hx < 0) {     /* x < -0.5 */
  53                 z = (one+x)*(float)0.5;
  54                 p = z*(pS0+z*(pS1+z*pS2));
  55                 q = one+z*qS1;
  56                 s = sqrtf(z);
  57                 r = p/q;
  58                 w = r*s-pio2_lo;
  59                 return pi - (float)2.0*(s+w);
  60         } else {                 /* x > 0.5 */
  61                 int32_t idf;
  62
  63                 z = (one-x)*(float)0.5;
  64                 s = sqrtf(z);
  65                 df = s;
  66                 GET_FLOAT_WORD(idf,df);
  67                 SET_FLOAT_WORD(df,idf&0xfffff000);
  68                 c  = (z-df*df)/(s+df);
  69                 p = z*(pS0+z*(pS1+z*pS2));
  70                 q = one+z*qS1;
  71                 r = p/q;
  72                 w = r*s+c;
  73                 return (float)2.0*(df+w);
  74         }
  75 }