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45 lines
1.2 KiB
C
45 lines
1.2 KiB
C
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/* -*- Mode: C; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
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*
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* The contents of this file are subject to the Netscape Public License
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* Version 1.0 (the "NPL"); you may not use this file except in
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* compliance with the NPL. You may obtain a copy of the NPL at
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* http://www.mozilla.org/NPL/
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*
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* Software distributed under the NPL is distributed on an "AS IS" basis,
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* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the NPL
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* for the specific language governing rights and limitations under the
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* NPL.
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*
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* The Initial Developer of this code under the NPL is Netscape
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* Communications Corporation. Portions created by Netscape are
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* Copyright (C) 1998 Netscape Communications Corporation. All Rights
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* Reserved.
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*/
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/*
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* Compute the log of the least power of 2 greater than or equal to n.
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*/
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#include "prtypes.h"
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PR_PUBLIC_API(int32)
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PR_CeilingLog2(uint32 n)
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{
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int32 log2;
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uint32 t;
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if (n == 0)
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return -1;
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log2 = (n & (n-1)) ? 1 : 0;
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if ((t = n >> 16) != 0)
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log2 += 16, n = t;
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if ((t = n >> 8) != 0)
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log2 += 8, n = t;
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if ((t = n >> 4) != 0)
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log2 += 4, n = t;
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if ((t = n >> 2) != 0)
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log2 += 2, n = t;
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if (n >> 1)
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log2++;
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return log2;
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}
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