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