/* Modified version of e_log.c for vbcc-PowerPC */

/*
 * ====================================================
 * 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.
 * ====================================================
 */

#include "vcmath.h"

static const double
  ln2_hi  =  6.93147180369123816490e-01,  /* 3fe62e42 fee00000 */
  ln2_lo  =  1.90821492927058770002e-10,  /* 3dea39ef 35793c76 */
  two54   =  1.80143985094819840000e+16,  /* 43500000 00000000 */
  Lg1 = 6.666666666666735130e-01,  /* 3FE55555 55555593 */
  Lg2 = 3.999999999940941908e-01,  /* 3FD99999 9997FA04 */
  Lg3 = 2.857142874366239149e-01,  /* 3FD24924 94229359 */
  Lg4 = 2.222219843214978396e-01,  /* 3FCC71C5 1D8E78AF */
  Lg5 = 1.818357216161805012e-01,  /* 3FC74664 96CB03DE */
  Lg6 = 1.531383769920937332e-01,  /* 3FC39A09 D078C69F */
  Lg7 = 1.479819860511658591e-01;  /* 3FC2F112 DF3E5244 */

static const double zero   =  0.0;


double log(double x)
{
  double hfsq,f,s,z,R,w,t1,t2,dk;
  long k=0,hx,i,j;
  unsigned long lx;

  hx = __get_high_word(&x);
  lx = __get_low_word(&x);

  if (hx < 0x00100000) {                  /* x < 2**-1022  */
    if (((hx&0x7fffffff)|lx)==0) 
      return -two54/zero;                 /* log(+-0)=-inf */
    if (hx<0)                             /* log(-#) = NaN */
      return (x-x)/zero;
    k -= 54; x *= two54;                  /* subnormal number, scale up x */
    hx = __get_high_word(&x);
  } 

  if (hx >= 0x7ff00000) return x+x;
  k += (hx>>20)-1023;
  hx &= 0x000fffff;
  i = (hx+0x95f64)&0x100000;
  __set_high_word(&x,hx|(i^0x3ff00000));  /* normalize x or x/2 */
  k += (i>>20);
  f = x-1.0;

  if((0x000fffff&(2+hx))<3) {             /* |f| < 2**-20 */
    if(f==zero) {
      if(k==0) return zero;
      else {
        dk=(double)k;
        return dk*ln2_hi+dk*ln2_lo;
      }
    }
    R = f*f*(0.5-0.33333333333333333*f);
    if(k==0) return f-R;
    else {
      dk=(double)k;
      return dk*ln2_hi-((R-dk*ln2_lo)-f);
    }
  }

  s = f/(2.0+f); 
  dk = (double)k;
  z = s*s;
  i = hx-0x6147a;
  w = z*z;
  j = 0x6b851-hx;
  t1= w*(Lg2+w*(Lg4+w*Lg6)); 
  t2= z*(Lg1+w*(Lg3+w*(Lg5+w*Lg7))); 
  i |= j;
  R = t2+t1;
  if(i>0) {
    hfsq=0.5*f*f;
    if(k==0) return f-(hfsq-s*(hfsq+R));
    else return dk*ln2_hi-((hfsq-(s*(hfsq+R)+dk*ln2_lo))-f);
  }
  else {
    if(k==0) return f-s*(f-R);
    else return dk*ln2_hi-((s*(f-R)-dk*ln2_lo)-f);
  }
}