dist/pdisk/bitfield.c

   1 //
   2 // bitfield.c - extract and set bit fields
   3 //
   4 // Written by Eryk Vershen
   5 //
   6 // See comments in bitfield.h
   7 //
   8
   9 /*
  10  * Copyright 1996, 1997 by Apple Computer, Inc.
  11  *              All Rights Reserved
  12  *
  13  * Permission to use, copy, modify, and distribute this software and
  14  * its documentation for any purpose and without fee is hereby granted,
  15  * provided that the above copyright notice appears in all copies and
  16  * that both the copyright notice and this permission notice appear in
  17  * supporting documentation.
  18  *
  19  * APPLE COMPUTER DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE
  20  * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  21  * FOR A PARTICULAR PURPOSE.
  22  *
  23  * IN NO EVENT SHALL APPLE COMPUTER BE LIABLE FOR ANY SPECIAL, INDIRECT, OR
  24  * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
  25  * LOSS OF USE, DATA OR PROFITS, WHETHER IN ACTION OF CONTRACT,
  26  * NEGLIGENCE, OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION
  27  * WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  28  */
  29
  30 #include "bitfield.h"
  31
  32
  33 //
  34 // Defines
  35 //
  36
  37
  38 //
  39 // Types
  40 //
  41
  42
  43 //
  44 // Global Constants
  45 //
  46 const unsigned long masks[] = {
  47     0x00000000,
  48     0x00000001, 0x00000003, 0x00000007, 0x0000000F,
  49     0x0000001F, 0x0000003F, 0x0000007F, 0x000000FF,
  50     0x000001FF, 0x000003FF, 0x000007FF, 0x00000FFF,
  51     0x00001FFF, 0x00003FFF, 0x00007FFF, 0x0000FFFF,
  52     0x0001FFFF, 0x0003FFFF, 0x0007FFFF, 0x000FFFFF,
  53     0x001FFFFF, 0x003FFFFF, 0x007FFFFF, 0x00FFFFFF,
  54     0x01FFFFFF, 0x03FFFFFF, 0x07FFFFFF, 0x0FFFFFFF,
  55     0x1FFFFFFF, 0x3FFFFFFF, 0x7FFFFFFF, 0xFFFFFFFF
  56 };
  57
  58
  59 //
  60 // Global Variables
  61 //
  62
  63
  64 //
  65 // Forward declarations
  66 //
  67
  68
  69 //
  70 // Routines
  71 //
  72 unsigned long
  73 bitfield_set(unsigned long *bf, int base, int length, unsigned long value)
  74 {
  75     unsigned long t;
  76     unsigned long m;
  77     int s;
  78
  79     // compute shift & mask, coerce value to correct number of bits,
  80     // zap the old bits and stuff the new value
  81     // return the masked value in case someone wants it.
  82     s = (base + 1) - length;
  83     m = masks[length];
  84     t = value & m;
  85     *bf = (*bf & ~(m << s)) | (t << s);
  86     return t;
  87 }
  88
  89
  90 unsigned long
  91 bitfield_get(unsigned long bf, int base, int length)
  92 {
  93     unsigned long m;
  94     int s;
  95
  96     // compute shift & mask
  97     // return the correct number of bits (shifted to low end)
  98     s = (base + 1) - length;
  99     m = masks[length];
 100     return ((bf >> s) & m);
 101 }