circular_iterator.h

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#pragma once

namespace cpp {

template<typename BI_ITERATOR>
BI_ITERATOR circularNext(BI_ITERATOR iBegin, BI_ITERATOR iEnd, BI_ITERATOR iCurr)
{
    if (iCurr == --iEnd)
        return iBegin;
    return ++iCurr;
}

template<typename BI_ITERATOR>
BI_ITERATOR circularPrior(BI_ITERATOR iBegin, BI_ITERATOR iEnd, BI_ITERATOR iCurr)
{
    if (iCurr == iBegin)
        return --iEnd;
    return --iCurr;
}

template<typename BI_ITERATOR, typename DISTANCE>
BI_ITERATOR circularAdvance(BI_ITERATOR iBegin, BI_ITERATOR iEnd,
                            BI_ITERATOR iCurr, DISTANCE d)
{
    const DISTANCE absD = d < 0 ? -d : d;
    for (DISTANCE i = 0; i < absD; ++i) {
        iCurr = d < 0 ? circularPrior(iBegin, iEnd, iCurr) :
                        circularNext(iBegin, iEnd, iCurr);
    }
    return iCurr;
}

} // namespace cpp