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

     /*-
      * SPDX-License-Identifier: BSD-3-Clause
      *
      * Copyright (c) 2004, 2005 David Young.  All rights reserved.
      *
      * Programmed for NetBSD by David Young.
      *
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. The name of David Young may not be used to endorse or promote
     *    products derived from this software without specific prior
     *    written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY David Young ``AS IS'' AND ANY
     * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
     * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
     * PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL David
     * Young BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
     * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
     * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
     * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
     * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
     * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
     * OF SUCH DAMAGE.
     *
     * $DragonFly: src/sys/dev/netif/bwi/bitops.h,v 1.1 2007/09/08 06:15:54 sephe Exp $
     * $FreeBSD$
     */
    
    #ifndef _BITOPS_H
    #define _BITOPS_H
    
    /*
     * __BIT(n): Return a bitmask with bit m set, where the least
     *           significant bit is bit 0.
     *
     * __BITS(m, n): Return a bitmask with bits m through n, inclusive,
     *               set.  It does not matter whether m>n or m<=n.  The
     *               least significant bit is bit 0.
     *
     * A "bitfield" is a span of consecutive bits defined by a bitmask,
     * where 1s select the bits in the bitfield.  __SHIFTIN, __SHIFTOUT,
     * and SHIFTOUT_MASK help read and write bitfields from device registers.
     *
     * __SHIFTIN(v, mask): Left-shift bits `v' into the bitfield
     *                     defined by `mask', and return them.  No
     *                     side-effects.
     *
     * __SHIFTOUT(v, mask): Extract and return the bitfield selected
     *                      by `mask' from `v', right-shifting the
     *                      bits so that the rightmost selected bit
     *                      is at bit 0.  No side-effects.
     *
     * __SHIFTOUT_MASK(mask): Right-shift the bits in `mask' so that
     *                        the rightmost non-zero bit is at bit
     *                        0.  This is useful for finding the
     *                        greatest unsigned value that a bitfield
     *                        can hold.  No side-effects.  Note that
     *                        SHIFTOUT_MASK(m) = SHIFTOUT(m, m).
     */
    
    /* __BIT(n): nth bit, where __BIT(0) == 0x1. */
    #define __BIT(__n) (((__n) == 32) ? 0 : ((uint32_t)1 << (__n)))
    
    /* __BITS(m, n): bits m through n, m < n. */
    #define __BITS(__m, __n)        \
            ((__BIT(MAX((__m), (__n)) + 1) - 1) ^ (__BIT(MIN((__m), (__n))) - 1))
    
    /* Find least significant bit that is set */
    #define __LOWEST_SET_BIT(__mask) ((((__mask) - 1) & (__mask)) ^ (__mask))
    
    #define __SHIFTOUT(__x, __mask) (((__x) & (__mask)) / __LOWEST_SET_BIT(__mask))
    #define __SHIFTIN(__x, __mask) ((__x) * __LOWEST_SET_BIT(__mask))
    #define __SHIFTOUT_MASK(__mask) __SHIFTOUT((__mask), (__mask))
    
    #endif  /* !_BITOPS_H */

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