ilogb.c raw

   1  #include <limits.h>
   2  #include "libm.h"
   3  
   4  int ilogb(double x)
   5  {
   6  	#pragma STDC FENV_ACCESS ON
   7  	union {double f; uint64_t i;} u = {x};
   8  	uint64_t i = u.i;
   9  	int e = i>>52 & 0x7ff;
  10  
  11  	if (!e) {
  12  		i <<= 12;
  13  		if (i == 0) {
  14  			FORCE_EVAL(0/0.0f);
  15  			return FP_ILOGB0;
  16  		}
  17  		/* subnormal x */
  18  		for (e = -0x3ff; i>>63 == 0; e--, i<<=1);
  19  		return e;
  20  	}
  21  	if (e == 0x7ff) {
  22  		FORCE_EVAL(0/0.0f);
  23  		return i<<12 ? FP_ILOGBNAN : INT_MAX;
  24  	}
  25  	return e - 0x3ff;
  26  }
  27