kc3-lang/SDL/src/libm/e_log10.c

Branch : - branch - v2.28 - tag -

• Show log

  Commit

• Author : Ethan Lee
  Date : 2018-01-17 11:53:09
  Hash : 11c348b4
  Message : SDL_log10

• src/libm/e_log10.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.
   * ====================================================
   */
  
  #if defined(_MSC_VER)           /* Handle Microsoft VC++ compiler specifics. */
  /* C4723: potential divide by zero. */
  #pragma warning ( disable : 4723 )
  #endif
  
  /* __ieee754_log10(x)
   * Return the base 10 logarithm of x
   *
   * Method :
   *	Let log10_2hi = leading 40 bits of log10(2) and
   *	    log10_2lo = log10(2) - log10_2hi,
   *	    ivln10   = 1/log(10) rounded.
   *	Then
   *		n = ilogb(x),
   *		if(n<0)  n = n+1;
   *		x = scalbn(x,-n);
   *		log10(x) := n*log10_2hi + (n*log10_2lo + ivln10*log(x))
   *
   * Note 1:
   *	To guarantee log10(10**n)=n, where 10**n is normal, the rounding
   *	mode must set to Round-to-Nearest.
   * Note 2:
   *	[1/log(10)] rounded to 53 bits has error  .198   ulps;
   *	log10 is monotonic at all binary break points.
   *
   * Special cases:
   *	log10(x) is NaN with signal if x < 0;
   *	log10(+INF) is +INF with no signal; log10(0) is -INF with signal;
   *	log10(NaN) is that NaN with no signal;
   *	log10(10**N) = N  for N=0,1,...,22.
   *
   * 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
  two54      =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
  ivln10     =  4.34294481903251816668e-01, /* 0x3FDBCB7B, 0x1526E50E */
  log10_2hi  =  3.01029995663611771306e-01, /* 0x3FD34413, 0x509F6000 */
  log10_2lo  =  3.69423907715893078616e-13; /* 0x3D59FEF3, 0x11F12B36 */
  
  static const double zero = 0.0;
  
  double attribute_hidden __ieee754_log10(double x)
  {
  	double y,z;
  	int32_t i,k,hx;
  	u_int32_t lx;
  
  	EXTRACT_WORDS(hx,lx,x);
  
          k=0;
          if (hx < 0x00100000) {                  /* x < 2**-1022  */
              if (((hx&0x7fffffff)|lx)==0)
                  return -two54/zero;             /* log(+-0)=-inf */
              if (hx<0) return (x-x)/zero;        /* log(-#) = NaN */
              k -= 54; x *= two54; /* subnormal number, scale up x */
  	    GET_HIGH_WORD(hx,x);
          }
  	if (hx >= 0x7ff00000) return x+x;
  	k += (hx>>20)-1023;
  	i  = ((u_int32_t)k&0x80000000)>>31;
          hx = (hx&0x000fffff)|((0x3ff-i)<<20);
          y  = (double)(k+i);
  	SET_HIGH_WORD(x,hx);
  	z  = y*log10_2lo + ivln10*__ieee754_log(x);
  	return  z+y*log10_2hi;
  }
  
  /*
   * wrapper log10(X)
   */
  #ifndef _IEEE_LIBM
  double log10(double x)
  {
  	double z = __ieee754_log10(x);
  	if (_LIB_VERSION == _IEEE_ || isnan(x))
  		return z;
  	if (x <= 0.0) {
  		if(x == 0.0)
  			return __kernel_standard(x, x, 18); /* log10(0) */
  		return __kernel_standard(x, x, 19); /* log10(x<0) */
  	}
  	return z;
  }
  #else
  strong_alias(__ieee754_log10, log10)
  #endif
  libm_hidden_def(log10)