lib/libm/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  * $FreeBSD: head/lib/msun/src/e_acosf.c 181257 2008-08-03 17:39:54Z das $
  16  */
  17
  18 #include "math.h"
  19 #include "math_private.h"
  20
  21 static const float
  22 one =  1.0000000000e+00, /* 0x3F800000 */
  23 pi =  3.1415925026e+00, /* 0x40490fda */
  24 pio2_hi =  1.5707962513e+00; /* 0x3fc90fda */
  25 static volatile float
  26 pio2_lo =  7.5497894159e-08; /* 0x33a22168 */
  27 static const float
  28 pS0 =  1.6666586697e-01,
  29 pS1 = -4.2743422091e-02,
  30 pS2 = -8.6563630030e-03,
  31 qS1 = -7.0662963390e-01;
  32
  33 float
  34 __ieee754_acosf(float x)
  35 {
  36         float z,p,q,r,w,s,c,df;
  37         int32_t hx,ix;
  38         GET_FLOAT_WORD(hx,x);
  39         ix = hx&0x7fffffff;
  40         if(ix>=0x3f800000) {            /* |x| >= 1 */
  41             if(ix==0x3f800000) {        /* |x| == 1 */
  42                 if(hx>0) return 0.0;    /* acos(1) = 0 */
  43                 else return pi+(float)2.0*pio2_lo;      /* acos(-1)= pi */
  44             }
  45             return (x-x)/(x-x);         /* acos(|x|>1) is NaN */
  46         }
  47         if(ix<0x3f000000) {     /* |x| < 0.5 */
  48             if(ix<=0x32800000) return pio2_hi+pio2_lo;/*if|x|<2**-26*/
  49             z = x*x;
  50             p = z*(pS0+z*(pS1+z*pS2));
  51             q = one+z*qS1;
  52             r = p/q;
  53             return pio2_hi - (x - (pio2_lo-x*r));
  54         } else  if (hx<0) {             /* x < -0.5 */
  55             z = (one+x)*(float)0.5;
  56             p = z*(pS0+z*(pS1+z*pS2));
  57             q = one+z*qS1;
  58             s = sqrtf(z);
  59             r = p/q;
  60             w = r*s-pio2_lo;
  61             return pi - (float)2.0*(s+w);
  62         } else {                        /* x > 0.5 */
  63             int32_t idf;
  64             z = (one-x)*(float)0.5;
  65             s = sqrtf(z);
  66             df = s;
  67             GET_FLOAT_WORD(idf,df);
  68             SET_FLOAT_WORD(df,idf&0xfffff000);
  69             c  = (z-df*df)/(s+df);
  70             p = z*(pS0+z*(pS1+z*pS2));
  71             q = one+z*qS1;
  72             r = p/q;
  73             w = r*s+c;
  74             return (float)2.0*(df+w);
  75         }
  76 }