1 /* 2 * CDDL HEADER START 3 * 4 * The contents of this file are subject to the terms of the 5 * Common Development and Distribution License (the "License"). 6 * You may not use this file except in compliance with the License. 7 * 8 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE 9 * or http://www.opensolaris.org/os/licensing. 10 * See the License for the specific language governing permissions 11 * and limitations under the License. 12 * 13 * When distributing Covered Code, include this CDDL HEADER in each 14 * file and include the License file at usr/src/OPENSOLARIS.LICENSE. 15 * If applicable, add the following below this CDDL HEADER, with the 16 * fields enclosed by brackets "[]" replaced with your own identifying 17 * information: Portions Copyright [yyyy] [name of copyright owner] 18 * 19 * CDDL HEADER END 20 */ 21 22 /* 23 * Copyright 2011 Nexenta Systems, Inc. All rights reserved. 24 */ 25 /* 26 * Copyright 2006 Sun Microsystems, Inc. All rights reserved. 27 * Use is subject to license terms. 28 */ 29 30 /* 31 * log2l(x) 32 * RETURN THE BASE 2 LOGARITHM OF X 33 * 34 * Method: 35 * purge off 0,INF, and NaN. 36 * n = ilogb(x) 37 * if (n<0) n+=1 38 * z = scalbn(x,-n) 39 * LOG2(x) = n + (1/ln2)*log(x) 40 */ 41 42 #pragma weak __log2l = log2l 43 44 #include "libm.h" 45 #include "longdouble.h" 46 47 static const long double 48 zero = 0.0L, 49 half = 0.5L, 50 one = 1.0L, 51 invln2 = 1.442695040888963407359924681001892137427e+0000L; 52 53 long double 54 log2l(long double x) { 55 int n; 56 57 if (x == zero || !finitel(x)) 58 return (logl(x)); 59 n = ilogbl(x); 60 if (n < 0) 61 n += 1; 62 x = scalbnl(x, -n); 63 if (x == half) 64 return (n - one); 65 return (n + invln2 * logl(x)); 66 } 67