lbug 0.16.1

An in-process property graph database management system built for query speed and scalability
Documentation 
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// Copyright 2016 The RE2 Authors.  All Rights Reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

#ifndef RE2_BITMAP256_H_
#define RE2_BITMAP256_H_

#ifdef _MSC_VER
#include <intrin.h>
#endif
#include <stdint.h>
#include <string.h>

#include "logging.h"
#include "util.h"

namespace lbug {
namespace regex {

class Bitmap256 {
public:
    Bitmap256() { Clear(); }

    // Clears all of the bits.
    void Clear() { memset(words_, 0, sizeof words_); }

    // Tests the bit with index c.
    bool Test(int c) const {
        DCHECK_GE(c, 0);
        DCHECK_LE(c, 255);

        return (words_[c / 64] & (1ULL << (c % 64))) != 0;
    }

    // Sets the bit with index c.
    void Set(int c) {
        DCHECK_GE(c, 0);
        DCHECK_LE(c, 255);

        words_[c / 64] |= (1ULL << (c % 64));
    }

    // Finds the next non-zero bit with index >= c.
    // Returns -1 if no such bit exists.
    int FindNextSetBit(int c) const;

private:
    // Finds the least significant non-zero bit in n.
    static int FindLSBSet(uint64_t n) {
        DCHECK_NE(n, 0);

#if defined(__GNUC__)
        return __builtin_ctzll(n);
#elif defined(_MSC_VER) && defined(_M_X64)
        unsigned long c;
        _BitScanForward64(&c, n);
        return static_cast<int>(c);
#elif defined(_MSC_VER) && defined(_M_IX86)
        unsigned long c;
        if (static_cast<uint32_t>(n) != 0) {
            _BitScanForward(&c, static_cast<uint32_t>(n));
            return static_cast<int>(c);
        } else {
            _BitScanForward(&c, static_cast<uint32_t>(n >> 32));
            return static_cast<int>(c) + 32;
        }
#else
        int c = 63;
        for (int shift = 1 << 5; shift != 0; shift >>= 1) {
            uint64_t word = n << shift;
            if (word != 0) {
                n = word;
                c -= shift;
            }
        }
        return c;
#endif
    }

    uint64_t words_[4];
};

int Bitmap256::FindNextSetBit(int c) const {
    DCHECK_GE(c, 0);
    DCHECK_LE(c, 255);

    // Check the word that contains the bit. Mask out any lower bits.
    int i = c / 64;
    uint64_t word = words_[i] & (~0ULL << (c % 64));
    if (word != 0)
        return (i * 64) + FindLSBSet(word);

    // Check any following words.
    i++;
    switch (i) {
    case 1:
        if (words_[1] != 0)
            return (1 * 64) + FindLSBSet(words_[1]);
        FALLTHROUGH_INTENDED;
    case 2:
        if (words_[2] != 0)
            return (2 * 64) + FindLSBSet(words_[2]);
        FALLTHROUGH_INTENDED;
    case 3:
        if (words_[3] != 0)
            return (3 * 64) + FindLSBSet(words_[3]);
        FALLTHROUGH_INTENDED;
    default:
        return -1;
    }
}

} // namespace regex
} // namespace lbug
#endif // RE2_BITMAP256_H_