/* @(#)s_logb.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.

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

 */

/*

 * double logb(x)

 * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.

 * Use ilogb instead.

 */

#include <math.h>

#include <math_private.h>

#include <libm-alias-double.h>

#include <fix-int-fp-convert-zero.h>

double

__logb (double x)

{

  int32_t lx, ix, rix;

  EXTRACT_WORDS (ix, lx, x);

  ix &= 0x7fffffff;             /* high |x| */

  if ((ix | lx) == 0)

    return -1.0 / fabs (x);

  if (ix >= 0x7ff00000)

    return x * x;

  if (__glibc_unlikely ((rix = ix >> 20) == 0))

    {

      /* POSIX specifies that denormal number is treated as

         though it were normalized.  */

      int ma;

      if (ix == 0)

	ma = __builtin_clz (lx) + 32;

      else

	ma = __builtin_clz (ix);

      rix -= ma - 12;

    }

  if (FIX_INT_FP_CONVERT_ZERO && rix == 1023)

    return 0.0;

  return (double) (rix - 1023);

}

#ifndef __logb

libm_alias_double (__logb, logb)

#endif