102 lines
2.3 KiB
C
102 lines
2.3 KiB
C
//
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// bitfield.c - extract and set bit fields
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//
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// Written by Eryk Vershen
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//
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// See comments in bitfield.h
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//
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/*
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* Copyright 1996, 1997 by Apple Computer, Inc.
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* All Rights Reserved
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*
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* Permission to use, copy, modify, and distribute this software and
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* its documentation for any purpose and without fee is hereby granted,
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* provided that the above copyright notice appears in all copies and
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* that both the copyright notice and this permission notice appear in
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* supporting documentation.
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*
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* APPLE COMPUTER DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE
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* INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE.
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*
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* IN NO EVENT SHALL APPLE COMPUTER BE LIABLE FOR ANY SPECIAL, INDIRECT, OR
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* CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
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* LOSS OF USE, DATA OR PROFITS, WHETHER IN ACTION OF CONTRACT,
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* NEGLIGENCE, OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION
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* WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*/
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#include "bitfield.h"
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//
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// Defines
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//
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//
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// Types
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//
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//
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// Global Constants
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//
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const unsigned long masks[] = {
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0x00000000,
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0x00000001, 0x00000003, 0x00000007, 0x0000000F,
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0x0000001F, 0x0000003F, 0x0000007F, 0x000000FF,
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0x000001FF, 0x000003FF, 0x000007FF, 0x00000FFF,
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0x00001FFF, 0x00003FFF, 0x00007FFF, 0x0000FFFF,
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0x0001FFFF, 0x0003FFFF, 0x0007FFFF, 0x000FFFFF,
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0x001FFFFF, 0x003FFFFF, 0x007FFFFF, 0x00FFFFFF,
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0x01FFFFFF, 0x03FFFFFF, 0x07FFFFFF, 0x0FFFFFFF,
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0x1FFFFFFF, 0x3FFFFFFF, 0x7FFFFFFF, 0xFFFFFFFF
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};
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//
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// Global Variables
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//
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//
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// Forward declarations
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//
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//
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// Routines
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//
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unsigned long
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bitfield_set(unsigned long *bf, int base, int length, unsigned long value)
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{
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unsigned long t;
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unsigned long m;
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int s;
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// compute shift & mask, coerce value to correct number of bits,
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// zap the old bits and stuff the new value
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// return the masked value in case someone wants it.
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s = (base + 1) - length;
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m = masks[length];
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t = value & m;
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*bf = (*bf & ~(m << s)) | (t << s);
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return t;
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}
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unsigned long
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bitfield_get(unsigned long bf, int base, int length)
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{
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unsigned long m;
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int s;
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// compute shift & mask
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// return the correct number of bits (shifted to low end)
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s = (base + 1) - length;
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m = masks[length];
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return ((bf >> s) & m);
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}
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