text: /*	$NetBSD: s_ilogbl.c,v 1.1 2011/07/28 22:32:29 joerg Exp $	*/
  
  /*-
   * Copyright (c) 2011 The NetBSD Foundation, Inc.
   * All rights reserved.
   *
   * This code is derived from software contributed to The NetBSD Foundation
   * by Joerg Sonnenberger.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   *
   * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
   * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
   * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
   * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
   * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
   * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
   * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
   * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   * POSSIBILITY OF SUCH DAMAGE.
   */
  
  #include <float.h>
  #include <math.h>
  #include <machine/ieee.h>
  
  #ifdef __HAVE_LONG_DOUBLE
  
  #if LDBL_MANT_DIG == 64
  #define	FROM_UNDERFLOW	0x1p65L
  #elif LDBL_MANT_DIG == 113
  #define	FROM_UNDERFLOW	0x1p114L
  #else
  #error Unsupported long double format
  #endif
  
  int
  ilogbl(long double x)
  {
  	union ieee_ext_u u;
  
  	if (x == 0.0L)
  		return 0x80000001;	/* ilogbl(0) = 0x80000001 */
  
  	u.extu_ld = x;
  
  	if (u.extu_ext.ext_exp == EXT_EXP_INFNAN)
  		return 0x7fffffff;
  
  	if (u.extu_ext.ext_exp == 0) {
  		/*
  		 * Scale denormalized numbers slightly,
  		 * so that they are normal.
  		 */
  		u.extu_ld *= FROM_UNDERFLOW;
  		return u.extu_ext.ext_exp - EXT_EXP_BIAS - LDBL_MANT_DIG - 1;
  	}
  	return u.extu_ext.ext_exp - EXT_EXP_BIAS;
  
  }
  
  #endif
  