nsz Git - musl/blob - src/math/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 <math.h>
  17 #include "math_private.h"
  18
  19 static const float
  20 one =  1.0000000000e+00, /* 0x3F800000 */
  21 pi =  3.1415925026e+00, /* 0x40490fda */
  22 pio2_hi =  1.5707962513e+00, /* 0x3fc90fda */
  23 pio2_lo =  7.5497894159e-08, /* 0x33a22168 */
  24 pS0 =  1.6666667163e-01, /* 0x3e2aaaab */
  25 pS1 = -3.2556581497e-01, /* 0xbea6b090 */
  26 pS2 =  2.0121252537e-01, /* 0x3e4e0aa8 */
  27 pS3 = -4.0055535734e-02, /* 0xbd241146 */
  28 pS4 =  7.9153501429e-04, /* 0x3a4f7f04 */
  29 pS5 =  3.4793309169e-05, /* 0x3811ef08 */
  30 qS1 = -2.4033949375e+00, /* 0xc019d139 */
  31 qS2 =  2.0209457874e+00, /* 0x4001572d */
  32 qS3 = -6.8828397989e-01, /* 0xbf303361 */
  33 qS4 =  7.7038154006e-02; /* 0x3d9dc62e */
  34
  35 float
  36 acosf(float x)
  37 {
  38         float z,p,q,r,w,s,c,df;
  39         int32_t hx,ix;
  40         GET_FLOAT_WORD(hx,x);
  41         ix = hx&0x7fffffff;
  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         } else if(ix>0x3f800000) {      /* |x| >= 1 */
  46             return (x-x)/(x-x);         /* acos(|x|>1) is NaN */
  47         }
  48         if(ix<0x3f000000) {     /* |x| < 0.5 */
  49             if(ix<=0x23000000) return pio2_hi+pio2_lo;/*if|x|<2**-57*/
  50             z = x*x;
  51             p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
  52             q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
  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+z*(pS3+z*(pS4+z*pS5)))));
  58             q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
  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+z*(pS3+z*(pS4+z*pS5)))));
  72             q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
  73             r = p/q;
  74             w = r*s+c;
  75             return (float)2.0*(df+w);
  76         }
  77 }