Segment.hpp

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00032 
00033 #ifndef MaximInterface_Segment
00034 #define MaximInterface_Segment
00035 
00036 #include <iterator>
00037 #include <utility>
00038 #include "type_traits.hpp"
00039 
00040 namespace MaximInterface {
00041 
00042 /// @brief
00043 /// Advances a given iterator by a given number of elements with bounds checking.
00044 /// @tparam InputIt Must meet the requirements of InputIterator.
00045 /// @param[in,out] it Iterator to advance. 
00046 /// @param bound
00047 /// Past-the-end boundary iterator. If distance is positive, bound must be
00048 /// reachable by incrementing the given iterator. If distance is negative, bound
00049 /// must be reachable by decrementing the given iterator.
00050 /// @param distance
00051 /// Number of elements to advance the given iterator. If distance is positive,
00052 /// the given iterator is incremented. If distance is negative, the given
00053 /// iterator is decremented, and InputIt must meet the requirements of
00054 /// BidirectionalIterator.
00055 /// @returns The number of elements that the given iterator was advanced.
00056 template <typename InputIt>
00057 typename std::iterator_traits<InputIt>::difference_type checkedAdvance(
00058     InputIt & it, const InputIt bound,
00059     typename std::iterator_traits<InputIt>::difference_type distance) {
00060   typedef
00061       typename std::iterator_traits<InputIt>::difference_type difference_type;
00062 
00063   // Use constant-time operations if InputIt is a random access iterator.
00064   if (is_same<typename std::iterator_traits<InputIt>::iterator_category,
00065               std::random_access_iterator_tag>::value) {
00066     const difference_type boundDistance = std::distance(it, bound);
00067     if (boundDistance >= 0) {
00068       if (distance > boundDistance) {
00069         distance = boundDistance;
00070       } else if (distance < 0) {
00071         distance = 0;
00072       }
00073     } else {
00074       if (distance < boundDistance) {
00075         distance = boundDistance;
00076       } else if (distance > 0) {
00077         distance = 0;
00078       }
00079     }
00080     std::advance(it, distance);
00081   } else {
00082     const difference_type startingDistance = distance;
00083     while (distance != 0 && it != bound) {
00084       if (distance > 0) {
00085         ++it;
00086         --distance;
00087       } else {
00088         --it;
00089         ++distance;
00090       }
00091     }
00092     if (startingDistance > 0) {
00093       distance = startingDistance - distance;
00094     } else {
00095       distance = startingDistance + distance;
00096     }
00097   }
00098   return distance;
00099 }
00100 
00101 /// @brief Locates an iterator sub-range using segment number addressing.
00102 /// @details
00103 /// Useful for devices that divide the memory space into uniform chunks such as
00104 /// pages and segments.
00105 /// @tparam ForwardIt Must meet the requirements of ForwardIterator.
00106 /// @param begin Beginning of the input data range.
00107 /// @param end End of the input data range.
00108 /// @param segmentSize Number of elements contained in a segment.
00109 /// @param segmentNum Zero-indexed number of the desired segment.
00110 /// @returns
00111 /// Pair of iterators representing the sub-range of the segment within
00112 /// the input range. If the segment does not exist within the input range, both
00113 /// iterators in the pair are set to the end iterator of the input range.
00114 template <typename ForwardIt, typename Index>
00115 std::pair<ForwardIt, ForwardIt> createSegment(
00116     ForwardIt begin, const ForwardIt end,
00117     const typename std::iterator_traits<ForwardIt>::difference_type segmentSize,
00118     Index segmentNum) {
00119   ForwardIt segmentEnd = begin;
00120   typename std::iterator_traits<ForwardIt>::difference_type lastSegmentSize =
00121       checkedAdvance(segmentEnd, end, segmentSize);
00122   while (segmentNum > 0 && segmentEnd != end) {
00123     begin = segmentEnd;
00124     lastSegmentSize = checkedAdvance(segmentEnd, end, segmentSize);
00125     --segmentNum;
00126   }
00127   if (segmentNum > 0 || lastSegmentSize != segmentSize) {
00128     begin = segmentEnd;
00129   }
00130   return std::make_pair(begin, segmentEnd);
00131 }
00132 
00133 } // namespace MaximInterface
00134 
00135 #endif