Back to index

lightning-sunbird  0.9+nobinonly
prlog2.c
Go to the documentation of this file.
00001 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
00002 /* ***** BEGIN LICENSE BLOCK *****
00003  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
00004  *
00005  * The contents of this file are subject to the Mozilla Public License Version
00006  * 1.1 (the "License"); you may not use this file except in compliance with
00007  * the License. You may obtain a copy of the License at
00008  * http://www.mozilla.org/MPL/
00009  *
00010  * Software distributed under the License is distributed on an "AS IS" basis,
00011  * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
00012  * for the specific language governing rights and limitations under the
00013  * License.
00014  *
00015  * The Original Code is the Netscape Portable Runtime (NSPR).
00016  *
00017  * The Initial Developer of the Original Code is
00018  * Netscape Communications Corporation.
00019  * Portions created by the Initial Developer are Copyright (C) 1998-2000
00020  * the Initial Developer. All Rights Reserved.
00021  *
00022  * Contributor(s):
00023  *
00024  * Alternatively, the contents of this file may be used under the terms of
00025  * either the GNU General Public License Version 2 or later (the "GPL"), or
00026  * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
00027  * in which case the provisions of the GPL or the LGPL are applicable instead
00028  * of those above. If you wish to allow use of your version of this file only
00029  * under the terms of either the GPL or the LGPL, and not to allow others to
00030  * use your version of this file under the terms of the MPL, indicate your
00031  * decision by deleting the provisions above and replace them with the notice
00032  * and other provisions required by the GPL or the LGPL. If you do not delete
00033  * the provisions above, a recipient may use your version of this file under
00034  * the terms of any one of the MPL, the GPL or the LGPL.
00035  *
00036  * ***** END LICENSE BLOCK ***** */
00037 
00038 #include "prbit.h"
00039 
00040 /*
00041 ** Compute the log of the least power of 2 greater than or equal to n
00042 */
00043 PR_IMPLEMENT(PRIntn) PR_CeilingLog2(PRUint32 n)
00044 {
00045     PRIntn log2 = 0;
00046 
00047     if (n & (n-1))
00048        log2++;
00049     if (n >> 16)
00050        log2 += 16, n >>= 16;
00051     if (n >> 8)
00052        log2 += 8, n >>= 8;
00053     if (n >> 4)
00054        log2 += 4, n >>= 4;
00055     if (n >> 2)
00056        log2 += 2, n >>= 2;
00057     if (n >> 1)
00058        log2++;
00059     return log2;
00060 }
00061 
00062 /*
00063 ** Compute the log of the greatest power of 2 less than or equal to n.
00064 ** This really just finds the highest set bit in the word.
00065 */
00066 PR_IMPLEMENT(PRIntn) PR_FloorLog2(PRUint32 n)
00067 {
00068     PRIntn log2 = 0;
00069 
00070     if (n >> 16)
00071        log2 += 16, n >>= 16;
00072     if (n >> 8)
00073        log2 += 8, n >>= 8;
00074     if (n >> 4)
00075        log2 += 4, n >>= 4;
00076     if (n >> 2)
00077        log2 += 2, n >>= 2;
00078     if (n >> 1)
00079        log2++;
00080     return log2;
00081 }