kc3-lang/SDL/src/libm/s_atan.c

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• Hash : e4146267
  Author :
  Date : 2013-11-16T18:56:02
  

  Fixed bug 2245 - add SDL_acos and SDL_asin Sylvain Here's some code to add arc cosine, and arc sin functions to SDL_stdlib.c There are plainly written using SDL_atan.

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• src/libm/s_atan.c

• /*
   * ====================================================
   * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   *
   * Developed at SunPro, a Sun Microsystems, Inc. business.
   * Permission to use, copy, modify, and distribute this
   * software is freely granted, provided that this notice
   * is preserved.
   * ====================================================
   */
  
  /* atan(x)
   * Method
   *   1. Reduce x to positive by atan(x) = -atan(-x).
   *   2. According to the integer k=4t+0.25 chopped, t=x, the argument
   *      is further reduced to one of the following intervals and the
   *      arctangent of t is evaluated by the corresponding formula:
   *
   *      [0,7/16]      atan(x) = t-t^3*(a1+t^2*(a2+...(a10+t^2*a11)...)
   *      [7/16,11/16]  atan(x) = atan(1/2) + atan( (t-0.5)/(1+t/2) )
   *      [11/16.19/16] atan(x) = atan( 1 ) + atan( (t-1)/(1+t) )
   *      [19/16,39/16] atan(x) = atan(3/2) + atan( (t-1.5)/(1+1.5t) )
   *      [39/16,INF]   atan(x) = atan(INF) + atan( -1/t )
   *
   * Constants:
   * The hexadecimal values are the intended ones for the following
   * constants. The decimal values may be used, provided that the
   * compiler will convert from decimal to binary accurately enough
   * to produce the hexadecimal values shown.
   */
  
  #include "math_libm.h"
  #include "math_private.h"
  
  static const double atanhi[] = {
    4.63647609000806093515e-01, /* atan(0.5)hi 0x3FDDAC67, 0x0561BB4F */
    7.85398163397448278999e-01, /* atan(1.0)hi 0x3FE921FB, 0x54442D18 */
    9.82793723247329054082e-01, /* atan(1.5)hi 0x3FEF730B, 0xD281F69B */
    1.57079632679489655800e+00, /* atan(inf)hi 0x3FF921FB, 0x54442D18 */
  };
  
  static const double atanlo[] = {
    2.26987774529616870924e-17, /* atan(0.5)lo 0x3C7A2B7F, 0x222F65E2 */
    3.06161699786838301793e-17, /* atan(1.0)lo 0x3C81A626, 0x33145C07 */
    1.39033110312309984516e-17, /* atan(1.5)lo 0x3C700788, 0x7AF0CBBD */
    6.12323399573676603587e-17, /* atan(inf)lo 0x3C91A626, 0x33145C07 */
  };
  
  static const double aT[] = {
    3.33333333333329318027e-01, /* 0x3FD55555, 0x5555550D */
   -1.99999999998764832476e-01, /* 0xBFC99999, 0x9998EBC4 */
    1.42857142725034663711e-01, /* 0x3FC24924, 0x920083FF */
   -1.11111104054623557880e-01, /* 0xBFBC71C6, 0xFE231671 */
    9.09088713343650656196e-02, /* 0x3FB745CD, 0xC54C206E */
   -7.69187620504482999495e-02, /* 0xBFB3B0F2, 0xAF749A6D */
    6.66107313738753120669e-02, /* 0x3FB10D66, 0xA0D03D51 */
   -5.83357013379057348645e-02, /* 0xBFADDE2D, 0x52DEFD9A */
    4.97687799461593236017e-02, /* 0x3FA97B4B, 0x24760DEB */
   -3.65315727442169155270e-02, /* 0xBFA2B444, 0x2C6A6C2F */
    1.62858201153657823623e-02, /* 0x3F90AD3A, 0xE322DA11 */
  };
  
  static const double
  one   = 1.0,
  huge   = 1.0e300;
  
  double atan(double x)
  {
  	double w,s1,s2,z;
  	int32_t ix,hx,id;
  
  	GET_HIGH_WORD(hx,x);
  	ix = hx&0x7fffffff;
  	if(ix>=0x44100000) {	/* if |x| >= 2^66 */
  	    u_int32_t low;
  	    GET_LOW_WORD(low,x);
  	    if(ix>0x7ff00000||
  		(ix==0x7ff00000&&(low!=0)))
  		return x+x;		/* NaN */
  	    if(hx>0) return  atanhi[3]+atanlo[3];
  	    else     return -atanhi[3]-atanlo[3];
  	} if (ix < 0x3fdc0000) {	/* |x| < 0.4375 */
  	    if (ix < 0x3e200000) {	/* |x| < 2^-29 */
  		if(huge+x>one) return x;	/* raise inexact */
  	    }
  	    id = -1;
  	} else {
  	x = fabs(x);
  	if (ix < 0x3ff30000) {		/* |x| < 1.1875 */
  	    if (ix < 0x3fe60000) {	/* 7/16 <=|x|<11/16 */
  		id = 0; x = (2.0*x-one)/(2.0+x);
  	    } else {			/* 11/16<=|x|< 19/16 */
  		id = 1; x  = (x-one)/(x+one);
  	    }
  	} else {
  	    if (ix < 0x40038000) {	/* |x| < 2.4375 */
  		id = 2; x  = (x-1.5)/(one+1.5*x);
  	    } else {			/* 2.4375 <= |x| < 2^66 */
  		id = 3; x  = -1.0/x;
  	    }
  	}}
      /* end of argument reduction */
  	z = x*x;
  	w = z*z;
      /* break sum from i=0 to 10 aT[i]z**(i+1) into odd and even poly */
  	s1 = z*(aT[0]+w*(aT[2]+w*(aT[4]+w*(aT[6]+w*(aT[8]+w*aT[10])))));
  	s2 = w*(aT[1]+w*(aT[3]+w*(aT[5]+w*(aT[7]+w*aT[9]))));
  	if (id<0) return x - x*(s1+s2);
  	else {
  	    z = atanhi[id] - ((x*(s1+s2) - atanlo[id]) - x);
  	    return (hx<0)? -z:z;
  	}
  }
  libm_hidden_def(atan)
  
  double SDL_acos(double val)
  {
      double result;
      if (val == -1.0) {
          result = M_PI;
      } else {
          result = SDL_atan(SDL_sqrt(1.0 - val * val) / val);
          if (result < 0.0)
          {
              result += M_PI;
          }
      }
      return result;
  }
  
  double SDL_asin(double val)
  {
      double result;
      if (val == -1.0) {
          result = -(M_PI / 2.0);
      } else {
          result = (M_PI / 2.0) - SDL_acos(val);
      }
      return result;
  }
  

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