125c28e83SPiotr Jasiukajtis /*
225c28e83SPiotr Jasiukajtis * CDDL HEADER START
325c28e83SPiotr Jasiukajtis *
425c28e83SPiotr Jasiukajtis * The contents of this file are subject to the terms of the
525c28e83SPiotr Jasiukajtis * Common Development and Distribution License (the "License").
625c28e83SPiotr Jasiukajtis * You may not use this file except in compliance with the License.
725c28e83SPiotr Jasiukajtis *
825c28e83SPiotr Jasiukajtis * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
925c28e83SPiotr Jasiukajtis * or http://www.opensolaris.org/os/licensing.
1025c28e83SPiotr Jasiukajtis * See the License for the specific language governing permissions
1125c28e83SPiotr Jasiukajtis * and limitations under the License.
1225c28e83SPiotr Jasiukajtis *
1325c28e83SPiotr Jasiukajtis * When distributing Covered Code, include this CDDL HEADER in each
1425c28e83SPiotr Jasiukajtis * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
1525c28e83SPiotr Jasiukajtis * If applicable, add the following below this CDDL HEADER, with the
1625c28e83SPiotr Jasiukajtis * fields enclosed by brackets "[]" replaced with your own identifying
1725c28e83SPiotr Jasiukajtis * information: Portions Copyright [yyyy] [name of copyright owner]
1825c28e83SPiotr Jasiukajtis *
1925c28e83SPiotr Jasiukajtis * CDDL HEADER END
2025c28e83SPiotr Jasiukajtis */
2125c28e83SPiotr Jasiukajtis
2225c28e83SPiotr Jasiukajtis /*
2325c28e83SPiotr Jasiukajtis * Copyright 2011 Nexenta Systems, Inc. All rights reserved.
2425c28e83SPiotr Jasiukajtis */
2525c28e83SPiotr Jasiukajtis /*
2625c28e83SPiotr Jasiukajtis * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
2725c28e83SPiotr Jasiukajtis * Use is subject to license terms.
2825c28e83SPiotr Jasiukajtis */
2925c28e83SPiotr Jasiukajtis
3025c28e83SPiotr Jasiukajtis /*
3125c28e83SPiotr Jasiukajtis * log2l(x)
3225c28e83SPiotr Jasiukajtis * RETURN THE BASE 2 LOGARITHM OF X
3325c28e83SPiotr Jasiukajtis *
3425c28e83SPiotr Jasiukajtis * Method:
3525c28e83SPiotr Jasiukajtis * purge off 0,INF, and NaN.
3625c28e83SPiotr Jasiukajtis * n = ilogb(x)
3725c28e83SPiotr Jasiukajtis * if (n<0) n+=1
3825c28e83SPiotr Jasiukajtis * z = scalbn(x,-n)
3925c28e83SPiotr Jasiukajtis * LOG2(x) = n + (1/ln2)*log(x)
4025c28e83SPiotr Jasiukajtis */
4125c28e83SPiotr Jasiukajtis
42*ddc0e0b5SRichard Lowe #pragma weak __log2l = log2l
4325c28e83SPiotr Jasiukajtis
4425c28e83SPiotr Jasiukajtis #include "libm.h"
4525c28e83SPiotr Jasiukajtis #include "longdouble.h"
4625c28e83SPiotr Jasiukajtis
4725c28e83SPiotr Jasiukajtis static const long double
4825c28e83SPiotr Jasiukajtis zero = 0.0L,
4925c28e83SPiotr Jasiukajtis half = 0.5L,
5025c28e83SPiotr Jasiukajtis one = 1.0L,
5125c28e83SPiotr Jasiukajtis invln2 = 1.442695040888963407359924681001892137427e+0000L;
5225c28e83SPiotr Jasiukajtis
5325c28e83SPiotr Jasiukajtis long double
log2l(long double x)5425c28e83SPiotr Jasiukajtis log2l(long double x) {
5525c28e83SPiotr Jasiukajtis int n;
5625c28e83SPiotr Jasiukajtis
5725c28e83SPiotr Jasiukajtis if (x == zero || !finitel(x))
5825c28e83SPiotr Jasiukajtis return (logl(x));
5925c28e83SPiotr Jasiukajtis n = ilogbl(x);
6025c28e83SPiotr Jasiukajtis if (n < 0)
6125c28e83SPiotr Jasiukajtis n += 1;
6225c28e83SPiotr Jasiukajtis x = scalbnl(x, -n);
6325c28e83SPiotr Jasiukajtis if (x == half)
6425c28e83SPiotr Jasiukajtis return (n - one);
6525c28e83SPiotr Jasiukajtis return (n + invln2 * logl(x));
6625c28e83SPiotr Jasiukajtis }
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