s_logb.c revision 15122:b211a52a7439
1/* 2 * Copyright (c) 1998, 2001, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26/* 27 * double logb(x) 28 * IEEE 754 logb. Included to pass IEEE test suite. Not recommend. 29 * Use ilogb instead. 30 */ 31 32#include "fdlibm.h" 33 34#ifdef __STDC__ 35 double logb(double x) 36#else 37 double logb(x) 38 double x; 39#endif 40{ 41 int lx,ix; 42 ix = (__HI(x))&0x7fffffff; /* high |x| */ 43 lx = __LO(x); /* low x */ 44 if((ix|lx)==0) return -1.0/fabs(x); 45 if(ix>=0x7ff00000) return x*x; 46 if((ix>>=20)==0) /* IEEE 754 logb */ 47 return -1022.0; 48 else 49 return (double) (ix-1023); 50} 51