newlib/libm/common/sf_logb.c

   1 /* 2009 for Newlib:  Sun's sf_ilogb.c converted to be sf_logb.c.  */
   2 /*
   3  * ====================================================
   4  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   5  *
   6  * Developed at SunPro, a Sun Microsystems, Inc. business.
   7  * Permission to use, copy, modify, and distribute this
   8  * software is freely granted, provided that this notice
   9  * is preserved.
  10  * ====================================================
  11  */
  12
  13 /* float logb(float x)
  14  * return the binary exponent of non-zero x
  15  * logbf(0) = -inf, raise divide-by-zero floating point exception
  16  * logbf(+inf|-inf) = +inf (no signal is raised)
  17  * logbf(NaN) = NaN (no signal is raised)
  18  * Per C99 recommendation, a NaN argument is returned unchanged.
  19  */
  20
  21 #include "fdlibm.h"
  22
  23 float
  24 #ifdef __STDC__
  25 logbf(float x)
  26 #else
  27 logbf(x)
  28 float x;
  29 #endif
  30 {
  31         __int32_t hx,ix;
  32
  33         GET_FLOAT_WORD(hx,x);
  34         hx &= 0x7fffffff;
  35         if(FLT_UWORD_IS_ZERO(hx))  {
  36                 float  xx;
  37                 /* arg==0:  return -inf and raise divide-by-zero exception */
  38                 SET_FLOAT_WORD(xx,hx);  /* +0.0 */
  39                 return -1./xx;  /* logbf(0) = -inf */
  40                 }
  41         if(FLT_UWORD_IS_SUBNORMAL(hx)) {
  42             for (ix = -126,hx<<=8; hx>0; hx<<=1) ix -=1;
  43             return (float) ix;
  44         }
  45         else if (FLT_UWORD_IS_INFINITE(hx)) return HUGE_VALF;   /* x==+|-inf */
  46         else if (FLT_UWORD_IS_NAN(hx)) return x;
  47         else return (float) ((hx>>23)-127);
  48 }
  49
  50 #ifdef _DOUBLE_IS_32BITS
  51
  52 #ifdef __STDC__
  53         double logb(double x)
  54 #else
  55         double logb(x)
  56         double x;
  57 #endif
  58 {
  59         return (double) logbf((float) x);
  60 }
  61
  62 #endif /* defined(_DOUBLE_IS_32BITS) */