The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/sys/bitops.h

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    1 /*
    2  * Copyright (c) 2004, 2005 David Young.  All rights reserved.
    3  *
    4  * Programmed for NetBSD by David Young.
    5  *
    6  * Redistribution and use in source and binary forms, with or without
    7  * modification, are permitted provided that the following conditions
    8  * are met:
    9  * 1. Redistributions of source code must retain the above copyright
   10  *    notice, this list of conditions and the following disclaimer.
   11  * 2. Redistributions in binary form must reproduce the above copyright
   12  *    notice, this list of conditions and the following disclaimer in the
   13  *    documentation and/or other materials provided with the distribution.
   14  * 3. The name of David Young may not be used to endorse or promote
   15  *    products derived from this software without specific prior
   16  *    written permission.
   17  *
   18  * THIS SOFTWARE IS PROVIDED BY David Young ``AS IS'' AND ANY
   19  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
   20  * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
   21  * PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL David
   22  * Young BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
   23  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
   24  * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   25  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
   26  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
   27  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
   29  * OF SUCH DAMAGE.
   30  *
   31  * $DragonFly: src/sys/sys/bitops.h,v 1.1 2007/10/14 04:15:17 sephe Exp $
   32  */
   33 
   34 #ifndef _SYS_BITOPS_H_
   35 #define _SYS_BITOPS_H_
   36 
   37 /*
   38  * __BIT(n): Return a bitmask with bit n set, where the least
   39  *           significant bit is bit 0.
   40  *
   41  * __BITS(m, n): Return a bitmask with bits m through n, inclusive,
   42  *               set.  It does not matter whether m>n or m<=n.  The
   43  *               least significant bit is bit 0.
   44  *
   45  * A "bitfield" is a span of consecutive bits defined by a bitmask,
   46  * where 1s select the bits in the bitfield.  __SHIFTIN, __SHIFTOUT,
   47  * and __SHIFTOUT_MASK help read and write bitfields from device
   48  * registers.
   49  *
   50  * __SHIFTIN(v, mask): Left-shift bits `v' into the bitfield
   51  *                     defined by `mask', and return them.  No
   52  *                     side-effects.
   53  *
   54  * __SHIFTOUT(v, mask): Extract and return the bitfield selected
   55  *                      by `mask' from `v', right-shifting the
   56  *                      bits so that the rightmost selected bit
   57  *                      is at bit 0.  No side-effects.
   58  *
   59  * __SHIFTOUT_MASK(mask): Right-shift the bits in `mask' so that
   60  *                        the rightmost non-zero bit is at bit
   61  *                        0.  This is useful for finding the
   62  *                        greatest unsigned value that a bitfield
   63  *                        can hold.  No side-effects.  Note that
   64  *                        __SHIFTOUT_MASK(m) = __SHIFTOUT(m, m).
   65  */
   66 
   67 /* __BIT(n): nth bit, where __BIT(0) == 0x1. */
   68 #define __BIT(__n) (((__n) == 32) ? 0 : ((uint32_t)1 << (__n)))
   69 #define __BIT64(__n) (((__n) == 64) ? 0 : ((uint64_t)1 << (__n)))
   70 
   71 /* __BITS(m, n): bits m through n, m < n. */
   72 #define __BITS(__m, __n)        \
   73         ((__BIT(MAX((__m), (__n)) + 1) - 1) ^ (__BIT(MIN((__m), (__n))) - 1))
   74 
   75 #define __BITS64(__m, __n)      \
   76         ((__BIT64(MAX((__m), (__n)) + 1) - 1) ^ \
   77          (__BIT64(MIN((__m), (__n))) - 1))
   78 
   79 /* Find least significant bit that is set */
   80 #define __LOWEST_SET_BIT(__mask) ((((__mask) - 1) & (__mask)) ^ (__mask))
   81 
   82 #define __SHIFTOUT(__x, __mask) (((__x) & (__mask)) / __LOWEST_SET_BIT(__mask))
   83 #define __SHIFTIN(__x, __mask) ((__x) * __LOWEST_SET_BIT(__mask))
   84 #define __SHIFTOUT_MASK(__mask) __SHIFTOUT((__mask), (__mask))
   85 
   86 #endif  /* !_SYS_BITOPS_H_ */

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