bit_buf.h

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/* Copyright (c) 2011 Wildfire Games
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
 * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

/*
 * FIFO bit queue
 */

#ifndef INCLUDED_ADTS_BIT_BUF
#define INCLUDED_ADTS_BIT_BUF

#include "lib/bits.h"

struct BitBuf
{
    uintptr_t buf;
    uintptr_t cur;  // bit to be appended (toggled by add())
    size_t len; // |buf| [bits]

    void reset()
    {
        buf = 0;
        cur = 0;
        len = 0;
    }

    // toggle current bit if desired, and add to buffer (new bit is LSB)
    void add(uintptr_t toggle)
    {
        cur ^= toggle;
        buf <<= 1;
        buf |= cur;
        len++;
    }

    // extract LS n bits
    size_t extract(uintptr_t n)
    {
        const uintptr_t bits = buf & bit_mask<uintptr_t>(n);
        buf >>= n;

        return bits;
    }
};

#endif  // #ifndef INCLUDED_ADTS_BIT_BUF