sys/sys/bitops.h

   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
  70 /* __BITS(m, n): bits m through n, m < n. */
  71 #define __BITS(__m, __n)        \
  72         ((__BIT(MAX((__m), (__n)) + 1) - 1) ^ (__BIT(MIN((__m), (__n))) - 1))
  73
  74 /* Find least significant bit that is set */
  75 #define __LOWEST_SET_BIT(__mask) ((((__mask) - 1) & (__mask)) ^ (__mask))
  76
  77 #define __SHIFTOUT(__x, __mask) (((__x) & (__mask)) / __LOWEST_SET_BIT(__mask))
  78 #define __SHIFTIN(__x, __mask) ((__x) * __LOWEST_SET_BIT(__mask))
  79 #define __SHIFTOUT_MASK(__mask) __SHIFTOUT((__mask), (__mask))
  80
  81 #endif  /* !_SYS_BITOPS_H_ */