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
  16 #include <sys/cdefs.h>
  17 #if defined(LIBM_SCCS) && !defined(lint)
  18 __RCSID("$NetBSD: e_acosf.c,v 1.8 2002/05/26 22:01:48 wiz Exp $");
  19 #endif
  20
  21 #include "math.h"
  22 #include "math_private.h"
  23
  24 static const float
  25 one =  1.0000000000e+00, /* 0x3F800000 */
  26 pi =  3.1415925026e+00, /* 0x40490fda */
  27 pio2_hi =  1.5707962513e+00, /* 0x3fc90fda */
  28 pio2_lo =  7.5497894159e-08, /* 0x33a22168 */
  29 pS0 =  1.6666667163e-01, /* 0x3e2aaaab */
  30 pS1 = -3.2556581497e-01, /* 0xbea6b090 */
  31 pS2 =  2.0121252537e-01, /* 0x3e4e0aa8 */
  32 pS3 = -4.0055535734e-02, /* 0xbd241146 */
  33 pS4 =  7.9153501429e-04, /* 0x3a4f7f04 */
  34 pS5 =  3.4793309169e-05, /* 0x3811ef08 */
  35 qS1 = -2.4033949375e+00, /* 0xc019d139 */
  36 qS2 =  2.0209457874e+00, /* 0x4001572d */
  37 qS3 = -6.8828397989e-01, /* 0xbf303361 */
  38 qS4 =  7.7038154006e-02; /* 0x3d9dc62e */
  39
  40 float
  41 __ieee754_acosf(float x)
  42 {
  43         float z,p,q,r,w,s,c,df;
  44         int32_t hx,ix;
  45         GET_FLOAT_WORD(hx,x);
  46         ix = hx&0x7fffffff;
  47         if(ix==0x3f800000) {            /* |x|==1 */
  48             if(hx>0) return 0.0;        /* acos(1) = 0  */
  49             else return pi+(float)2.0*pio2_lo;  /* acos(-1)= pi */
  50         } else if(ix>0x3f800000) {      /* |x| >= 1 */
  51             return (x-x)/(x-x);         /* acos(|x|>1) is NaN */
  52         }
  53         if(ix<0x3f000000) {     /* |x| < 0.5 */
  54             if(ix<=0x23000000) return pio2_hi+pio2_lo;/*if|x|<2**-57*/
  55             z = x*x;
  56             p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
  57             q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
  58             r = p/q;
  59             return pio2_hi - (x - (pio2_lo-x*r));
  60         } else  if (hx<0) {             /* x < -0.5 */
  61             z = (one+x)*(float)0.5;
  62             p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
  63             q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
  64             s = __ieee754_sqrtf(z);
  65             r = p/q;
  66             w = r*s-pio2_lo;
  67             return pi - (float)2.0*(s+w);
  68         } else {                        /* x > 0.5 */
  69             int32_t idf;
  70             z = (one-x)*(float)0.5;
  71             s = __ieee754_sqrtf(z);
  72             df = s;
  73             GET_FLOAT_WORD(idf,df);
  74             SET_FLOAT_WORD(df,idf&0xfffff000);
  75             c  = (z-df*df)/(s+df);
  76             p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
  77             q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
  78             r = p/q;
  79             w = r*s+c;
  80             return (float)2.0*(df+w);
  81         }
  82 }