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  1. /* ef_log.c -- float version of e_log.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 "fdlibm.h"
  17.  
  18. #ifdef __STDC__
  19. static const float
  20. #else
  21. static float
  22. #endif
  23. ln2_hi =   6.9313812256e-01,    /* 0x3f317180 */
  24. ln2_lo =   9.0580006145e-06,    /* 0x3717f7d1 */
  25. two25 =    3.355443200e+07,     /* 0x4c000000 */
  26. Lg1 = 6.6666668653e-01, /* 3F2AAAAB */
  27. Lg2 = 4.0000000596e-01, /* 3ECCCCCD */
  28. Lg3 = 2.8571429849e-01, /* 3E924925 */
  29. Lg4 = 2.2222198546e-01, /* 3E638E29 */
  30. Lg5 = 1.8183572590e-01, /* 3E3A3325 */
  31. Lg6 = 1.5313838422e-01, /* 3E1CD04F */
  32. Lg7 = 1.4798198640e-01; /* 3E178897 */
  33.  
  34. #ifdef __STDC__
  35. static const float zero   =  0.0;
  36. #else
  37. static float zero   =  0.0;
  38. #endif
  39.  
  40. #ifdef __STDC__
  41.         float __ieee754_logf(float x)
  42. #else
  43.         float __ieee754_logf(x)
  44.         float x;
  45. #endif
  46. {
  47.         float hfsq,f,s,z,R,w,t1,t2,dk;
  48.         __int32_t k,ix,i,j;
  49.  
  50.         GET_FLOAT_WORD(ix,x);
  51.  
  52.         k=0;
  53.         if (FLT_UWORD_IS_ZERO(ix&0x7fffffff))
  54.             return -two25/zero;         /* log(+-0)=-inf */
  55.         if (ix<0) return (x-x)/zero;    /* log(-#) = NaN */
  56.         if (!FLT_UWORD_IS_FINITE(ix)) return x+x;
  57.         if (FLT_UWORD_IS_SUBNORMAL(ix)) {
  58.             k -= 25; x *= two25; /* subnormal number, scale up x */
  59.             GET_FLOAT_WORD(ix,x);
  60.         }
  61.         k += (ix>>23)-127;
  62.         ix &= 0x007fffff;
  63.         i = (ix+(0x95f64<<3))&0x800000;
  64.         SET_FLOAT_WORD(x,ix|(i^0x3f800000));    /* normalize x or x/2 */
  65.         k += (i>>23);
  66.         f = x-(float)1.0;
  67.         if((0x007fffff&(15+ix))<16) {   /* |f| < 2**-20 */
  68.            if(f==zero) { if(k==0) return zero;  else {dk=(float)k;
  69.                                 return dk*ln2_hi+dk*ln2_lo;}}
  70.             R = f*f*((float)0.5-(float)0.33333333333333333*f);
  71.             if(k==0) return f-R; else {dk=(float)k;
  72.                      return dk*ln2_hi-((R-dk*ln2_lo)-f);}
  73.         }
  74.         s = f/((float)2.0+f);
  75.         dk = (float)k;
  76.         z = s*s;
  77.         i = ix-(0x6147a<<3);
  78.         w = z*z;
  79.         j = (0x6b851<<3)-ix;
  80.         t1= w*(Lg2+w*(Lg4+w*Lg6));
  81.         t2= z*(Lg1+w*(Lg3+w*(Lg5+w*Lg7)));
  82.         i |= j;
  83.         R = t2+t1;
  84.         if(i>0) {
  85.             hfsq=(float)0.5*f*f;
  86.             if(k==0) return f-(hfsq-s*(hfsq+R)); else
  87.                      return dk*ln2_hi-((hfsq-(s*(hfsq+R)+dk*ln2_lo))-f);
  88.         } else {
  89.             if(k==0) return f-s*(f-R); else
  90.                      return dk*ln2_hi-((s*(f-R)-dk*ln2_lo)-f);
  91.         }
  92. }
  93.