pjs/js/src/jslog2.c

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2.3 KiB
C

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/*
* The contents of this file are subject to the Netscape Public
* License Version 1.1 (the "License"); you may not use this file
* except in compliance with the License. You may obtain a copy of
* the License at http://www.mozilla.org/NPL/
*
* Software distributed under the License is distributed on an "AS
* IS" basis, WITHOUT WARRANTY OF ANY KIND, either express oqr
* implied. See the License for the specific language governing
* rights and limitations under the License.
*
* The Original Code is Mozilla Communicator client code, released
* March 31, 1998.
*
* The Initial Developer of the Original Code is Netscape
* Communications Corporation. Portions created by Netscape are
* Copyright (C) 1998 Netscape Communications Corporation. All
* Rights Reserved.
*
* Contributor(s):
*
* Alternatively, the contents of this file may be used under the
* terms of the GNU Public License (the "GPL"), in which case the
* provisions of the GPL are applicable instead of those above.
* If you wish to allow use of your version of this file only
* under the terms of the GPL and not to allow others to use your
* version of this file under the NPL, indicate your decision by
* deleting the provisions above and replace them with the notice
* and other provisions required by the GPL. If you do not delete
* the provisions above, a recipient may use your version of this
* file under either the NPL or the GPL.
*/
#include "jsbit.h"
/*
** Compute the log of the least power of 2 greater than or equal to n
*/
JS_PUBLIC_API(JSIntn) JS_CeilingLog2(JSUint32 n)
{
JSIntn log2 = 0;
if (n & (n-1))
log2++;
if (n >> 16)
log2 += 16, n >>= 16;
if (n >> 8)
log2 += 8, n >>= 8;
if (n >> 4)
log2 += 4, n >>= 4;
if (n >> 2)
log2 += 2, n >>= 2;
if (n >> 1)
log2++;
return log2;
}
/*
** Compute the log of the greatest power of 2 less than or equal to n.
** This really just finds the highest set bit in the word.
*/
JS_PUBLIC_API(JSIntn) JS_FloorLog2(JSUint32 n)
{
JSIntn log2 = 0;
if (n >> 16)
log2 += 16, n >>= 16;
if (n >> 8)
log2 += 8, n >>= 8;
if (n >> 4)
log2 += 4, n >>= 4;
if (n >> 2)
log2 += 2, n >>= 2;
if (n >> 1)
log2++;
return log2;
}