src/core/common/binary_search.cpp

/*
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 *     derived from this software without specific prior written permission.
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 *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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 */

/**
 * @file
 *  This file implements a generic binary search.
 */

#include "binary_search.hpp"

#include "common/code_utils.hpp"

namespace ot {

const void *BinarySearch::Find(const void *aKey,
                               const void *aTable,
                               uint16_t    aLength,
                               uint16_t    aEntrySize,
                               Comparator  aComparator)
{
    const void *entry;
    uint16_t    left  = 0;
    uint16_t    right = aLength;

    while (left < right)
    {
        uint16_t middle = (left + right) / 2;
        int      compare;

        // Note that `aTable` array entry type is not known here and
        // only its size is given as `aEntrySize`. Based on this, we
        // can calculate the pointer to the table entry at any index
        // (such as `[middle]`) which is then passed to the given
        // `aComparator` function which knows how to cast the void
        // pointer to proper entry type and compare it with `aKey`.
        // This model keeps the implementation generic and reusable
        // allowing it to be used with any entry type.

        entry = reinterpret_cast<const uint8_t *>(aTable) + aEntrySize * middle;

        compare = aComparator(aKey, entry);

        if (compare == 0)
        {
            ExitNow();
        }
        else if (compare > 0)
        {
            left = middle + 1;
        }
        else
        {
            right = middle;
        }
    }

    entry = nullptr;

exit:
    return entry;
}

} // namespace ot