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   1 /* ef_acos.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 "fdlibm.h"
  17
  18 #ifdef __STDC__
  19 static const float
  20 #else
  21 static float
  22 #endif
  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 #ifdef __STDC__
  39         float __ieee754_acosf(float x)
  40 #else
  41         float __ieee754_acosf(x)
  42         float x;
  43 #endif
  44 {
  45         float z,p,q,r,w,s,c,df;
  46         __int32_t hx,ix;
  47         GET_FLOAT_WORD(hx,x);
  48         ix = hx&0x7fffffff;
  49         if(ix==0x3f800000) {            /* |x|==1 */
  50             if(hx>0) return 0.0;        /* acos(1) = 0  */
  51             else return pi+(float)2.0*pio2_lo;  /* acos(-1)= pi */
  52         } else if(ix>0x3f800000) {      /* |x| >= 1 */
  53             return (x-x)/(x-x);         /* acos(|x|>1) is NaN */
  54         }
  55         if(ix<0x3f000000) {     /* |x| < 0.5 */
  56             if(ix<=0x23000000) return pio2_hi+pio2_lo;/*if|x|<2**-57*/
  57             z = x*x;
  58             p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
  59             q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
  60             r = p/q;
  61             return pio2_hi - (x - (pio2_lo-x*r));
  62         } else  if (hx<0) {             /* x < -0.5 */
  63             z = (one+x)*(float)0.5;
  64             p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
  65             q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
  66             s = __ieee754_sqrtf(z);
  67             r = p/q;
  68             w = r*s-pio2_lo;
  69             return pi - (float)2.0*(s+w);
  70         } else {                        /* x > 0.5 */
  71             __int32_t idf;
  72             z = (one-x)*(float)0.5;
  73             s = __ieee754_sqrtf(z);
  74             df = s;
  75             GET_FLOAT_WORD(idf,df);
  76             SET_FLOAT_WORD(df,idf&0xfffff000);
  77             c  = (z-df*df)/(s+df);
  78             p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
  79             q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
  80             r = p/q;
  81             w = r*s+c;
  82             return (float)2.0*(df+w);
  83         }
  84 }