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  * $NetBSD: e_acosf.c,v 1.8 2002/05/26 22:01:48 wiz Exp $
  16  * $DragonFly: src/lib/libm/src/e_acosf.c,v 1.1 2005/07/26 21:15:20 joerg Exp $
  17  */
  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 pio2_lo =  7.5497894159e-08, /* 0x33a22168 */
  27 pS0 =  1.6666667163e-01, /* 0x3e2aaaab */
  28 pS1 = -3.2556581497e-01, /* 0xbea6b090 */
  29 pS2 =  2.0121252537e-01, /* 0x3e4e0aa8 */
  30 pS3 = -4.0055535734e-02, /* 0xbd241146 */
  31 pS4 =  7.9153501429e-04, /* 0x3a4f7f04 */
  32 pS5 =  3.4793309169e-05, /* 0x3811ef08 */
  33 qS1 = -2.4033949375e+00, /* 0xc019d139 */
  34 qS2 =  2.0209457874e+00, /* 0x4001572d */
  35 qS3 = -6.8828397989e-01, /* 0xbf303361 */
  36 qS4 =  7.7038154006e-02; /* 0x3d9dc62e */
  37
  38 float
  39 acosf(float x)
  40 {
  41         float z,p,q,r,w,s,c,df;
  42         int32_t hx,ix;
  43         GET_FLOAT_WORD(hx,x);
  44         ix = hx&0x7fffffff;
  45         if(ix==0x3f800000) {            /* |x|==1 */
  46             if(hx>0) return 0.0;        /* acos(1) = 0  */
  47             else return pi+(float)2.0*pio2_lo;  /* acos(-1)= pi */
  48         } else if(ix>0x3f800000) {      /* |x| >= 1 */
  49             return (x-x)/(x-x);         /* acos(|x|>1) is NaN */
  50         }
  51         if(ix<0x3f000000) {     /* |x| < 0.5 */
  52             if(ix<=0x23000000) return pio2_hi+pio2_lo;/*if|x|<2**-57*/
  53             z = x*x;
  54             p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
  55             q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
  56             r = p/q;
  57             return pio2_hi - (x - (pio2_lo-x*r));
  58         } else  if (hx<0) {             /* x < -0.5 */
  59             z = (one+x)*(float)0.5;
  60             p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
  61             q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
  62             s = sqrtf(z);
  63             r = p/q;
  64             w = r*s-pio2_lo;
  65             return pi - (float)2.0*(s+w);
  66         } else {                        /* x > 0.5 */
  67             int32_t idf;
  68             z = (one-x)*(float)0.5;
  69             s = sqrtf(z);
  70             df = s;
  71             GET_FLOAT_WORD(idf,df);
  72             SET_FLOAT_WORD(df,idf&0xfffff000);
  73             c  = (z-df*df)/(s+df);
  74             p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
  75             q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
  76             r = p/q;
  77             w = r*s+c;
  78             return (float)2.0*(df+w);
  79         }
  80 }