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  1. /* Copyright (C) 1994 DJ Delorie, see COPYING.DJ for details */
  2. /* e_acosf.c -- float version of e_acos.c.
  3.  * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
  4.  */
  5.  
  6. /*
  7.  * ====================================================
  8.  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
  9.  *
  10.  * Developed at SunPro, a Sun Microsystems, Inc. business.
  11.  * Permission to use, copy, modify, and distribute this
  12.  * software is freely granted, provided that this notice
  13.  * is preserved.
  14.  * ====================================================
  15.  */
  16.  
  17. #if defined(LIBM_SCCS) && !defined(lint)
  18. static char rcsid[] = "$Id: e_acosf.c,v 1.2 1994/08/18 23:04:53 jtc Exp $";
  19. #endif
  20.  
  21. #include "math.h"
  22. #include "math_private.h"
  23.  
  24. #ifdef __STDC__
  25. static const float
  26. #else
  27. static float
  28. #endif
  29. one =  1.0000000000e+00, /* 0x3F800000 */
  30. pi =  3.1415925026e+00, /* 0x40490fda */
  31. pio2_hi =  1.5707962513e+00, /* 0x3fc90fda */
  32. pio2_lo =  7.5497894159e-08, /* 0x33a22168 */
  33. pS0 =  1.6666667163e-01, /* 0x3e2aaaab */
  34. pS1 = -3.2556581497e-01, /* 0xbea6b090 */
  35. pS2 =  2.0121252537e-01, /* 0x3e4e0aa8 */
  36. pS3 = -4.0055535734e-02, /* 0xbd241146 */
  37. pS4 =  7.9153501429e-04, /* 0x3a4f7f04 */
  38. pS5 =  3.4793309169e-05, /* 0x3811ef08 */
  39. qS1 = -2.4033949375e+00, /* 0xc019d139 */
  40. qS2 =  2.0209457874e+00, /* 0x4001572d */
  41. qS3 = -6.8828397989e-01, /* 0xbf303361 */
  42. qS4 =  7.7038154006e-02; /* 0x3d9dc62e */
  43.  
  44. #ifdef __STDC__
  45.         float __ieee754_acosf(float x)
  46. #else
  47.         float __ieee754_acosf(x)
  48.         float x;
  49. #endif
  50. {
  51.         float z,p,q,r,w,s,c,df;
  52.         int32_t hx,ix;
  53.         GET_FLOAT_WORD(hx,x);
  54.         ix = hx&0x7fffffff;
  55.         if(ix==0x3f800000) {            /* |x|==1 */
  56.             if(hx>0) return 0.0;        /* acos(1) = 0  */
  57.             else return pi+(float)2.0*pio2_lo;  /* acos(-1)= pi */
  58.         } else if(ix>0x3f800000) {      /* |x| >= 1 */
  59.             return (x-x)/(x-x);         /* acos(|x|>1) is NaN */
  60.         }
  61.         if(ix<0x3f000000) {     /* |x| < 0.5 */
  62.             if(ix<=0x23000000) return pio2_hi+pio2_lo;/*if|x|<2**-57*/
  63.             z = x*x;
  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.             r = p/q;
  67.             return pio2_hi - (x - (pio2_lo-x*r));
  68.         } else  if (hx<0) {             /* x < -0.5 */
  69.             z = (one+x)*(float)0.5;
  70.             p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
  71.             q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
  72.             s = sqrtf(z);
  73.             r = p/q;
  74.             w = r*s-pio2_lo;
  75.             return pi - (float)2.0*(s+w);
  76.         } else {                        /* x > 0.5 */
  77.             int32_t idf;
  78.             z = (one-x)*(float)0.5;
  79.             s = sqrtf(z);
  80.             df = s;
  81.             GET_FLOAT_WORD(idf,df);
  82.             SET_FLOAT_WORD(df,idf&0xfffff000);
  83.             c  = (z-df*df)/(s+df);
  84.             p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
  85.             q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
  86.             r = p/q;
  87.             w = r*s+c;
  88.             return (float)2.0*(df+w);
  89.         }
  90. }
  91.