/* @(#)s_ilogb.c 5.1 93/09/24 */

/*

 * ====================================================

 * 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(LIBM_SCCS) && !defined(lint)

static char rcsid[] = "$NetBSD: s_ilogb.c,v 1.9 1995/05/10 20:47:28 jtc Exp $";

#endif

/* ilogb(double x)

 * return the binary exponent of non-zero x

 * ilogb(0) = FP_ILOGB0

 * ilogb(NaN) = FP_ILOGBNAN (no signal is raised)

 * ilogb(+-Inf) = INT_MAX (no signal is raised)

 */

#include <limits.h>

#include <math.h>

#include <math_private.h>

int

__ieee754_ilogb (double x)

{

  int32_t hx, lx, ix;

  GET_HIGH_WORD (hx, x);

  hx &= 0x7fffffff;

  if (hx < 0x00100000)

    {

      GET_LOW_WORD (lx, x);

      if ((hx | lx) == 0)

	return FP_ILOGB0;               /* ilogb(0) = FP_ILOGB0 */

      else                              /* subnormal x */

      if (hx == 0)

	{

	  for (ix = -1043; lx > 0; lx <<= 1)

	    ix -= 1;

	}

      else

	{

	  for (ix = -1022, hx <<= 11; hx > 0; hx <<= 1)

	    ix -= 1;

	}

      return ix;

    }

  else if (hx < 0x7ff00000)

    return (hx >> 20) - 1023;

  else if (FP_ILOGBNAN != INT_MAX)

    {

      /* ISO C99 requires ilogb(+-Inf) == INT_MAX.  */

      GET_LOW_WORD (lx, x);

      if (((hx ^ 0x7ff00000) | lx) == 0)

	return INT_MAX;

    }

  return FP_ILOGBNAN;

}