lib/msun/src/e_acosf.c

   1 /* e_acosf.c -- float version of e_acos.c.
   2  * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
   3  */
   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 <sys/cdefs.h>
  17 __FBSDID("$FreeBSD$");
  18
  19 #include "math.h"
  20 #include "math_private.h"
  21
  22 static const float
  23 one =  1.0000000000e+00, /* 0x3F800000 */
  24 pi =  3.1415925026e+00, /* 0x40490fda */
  25 pio2_hi =  1.5707962513e+00; /* 0x3fc90fda */
  26 static volatile float
  27 pio2_lo =  7.5497894159e-08; /* 0x33a22168 */
  28 static const float
  29 pS0 =  1.6666586697e-01,
  30 pS1 = -4.2743422091e-02,
  31 pS2 = -8.6563630030e-03,
  32 qS1 = -7.0662963390e-01;
  33
  34 float
  35 __ieee754_acosf(float x)
  36 {
  37         float z,p,q,r,w,s,c,df;
  38         int32_t hx,ix;
  39         GET_FLOAT_WORD(hx,x);
  40         ix = hx&0x7fffffff;
  41         if(ix>=0x3f800000) {            /* |x| >= 1 */
  42             if(ix==0x3f800000) {        /* |x| == 1 */
  43                 if(hx>0) return 0.0;    /* acos(1) = 0 */
  44                 else return pi+(float)2.0*pio2_lo;      /* acos(-1)= pi */
  45             }
  46             return (x-x)/(x-x);         /* acos(|x|>1) is NaN */
  47         }
  48         if(ix<0x3f000000) {     /* |x| < 0.5 */
  49             if(ix<=0x32800000) return pio2_hi+pio2_lo;/*if|x|<2**-26*/
  50             z = x*x;
  51             p = z*(pS0+z*(pS1+z*pS2));
  52             q = one+z*qS1;
  53             r = p/q;
  54             return pio2_hi - (x - (pio2_lo-x*r));
  55         } else  if (hx<0) {             /* x < -0.5 */
  56             z = (one+x)*(float)0.5;
  57             p = z*(pS0+z*(pS1+z*pS2));
  58             q = one+z*qS1;
  59             s = sqrtf(z);
  60             r = p/q;
  61             w = r*s-pio2_lo;
  62             return pi - (float)2.0*(s+w);
  63         } else {                        /* x > 0.5 */
  64             int32_t idf;
  65             z = (one-x)*(float)0.5;
  66             s = sqrtf(z);
  67             df = s;
  68             GET_FLOAT_WORD(idf,df);
  69             SET_FLOAT_WORD(df,idf&0xfffff000);
  70             c  = (z-df*df)/(s+df);
  71             p = z*(pS0+z*(pS1+z*pS2));
  72             q = one+z*qS1;
  73             r = p/q;
  74             w = r*s+c;
  75             return (float)2.0*(df+w);
  76         }
  77 }