xref: /src/lib/libm/noieee_src/n_log2.c

/*      $NetBSD: n_log2.c,v 1.2 2024/07/16 14:52:50 riastradh Exp $ */
/*-
 * Copyright (c) 2014 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Martin Husemann <martin@NetBSD.org>.
 *
 * 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 <sys/cdefs.h>
__RCSID("$NetBSD: n_log2.c,v 1.2 2024/07/16 14:52:50 riastradh Exp $");

/* LOG2(X)
 * RETURN THE BASE 10 LOGARITHM OF x
 *
 * Required kernel function:
 *	log(x)
 *
 * Method :
 *			    log(x)
 *		log2(x) =  ---------
 *			    log(2)
 */

#include "namespace.h"

#define _LIBM_STATIC
#include "mathimpl.h"

__weak_alias(log2l, _log2l)
__strong_alias(_log2l, _log2)

static const double ln2 = .6931471805599453094172321214581765680755;

__weak_alias(log2, _log2)
double
log2(double x)
{
	return log(x)/ln2;
}

__weak_alias(log2f, _log2f)
float
log2f(float x)
{
	return logf(x)/ln2;
}