Sux Documentation

Welcome to the C++ part of the Sux project.

Available classes

The classes we provide fall into three categories:

All classes are heavily asserted. For testing speed, remember to use -DNDEBUG.

All provided classes are templates, so you just have to copy the files in the sux directory somewhere in your include path.


  • Assuming v is a bit vector represented by an array of uint64_t and n is the number of bits represented therein,

      #include <sux/bits/Rank9Sel.hpp>
      sux::bits::Rank9Sel rs(v, n);

    will create a rank/select structure using Rank9 and Select9. Note that the bit vector is not copied, so if you change its contents the results will be unpredictable.

  • Assuming again that v is a bit vector and n the number of bits represented therein, to create a dynamic rank/select data structure using a fixed-size Fenwick tree in classical Fenwick layout over strides of sixteen words you must use

      #include <sux/bits/StrideDynRankSel.hpp>
      #include <sux/util/FenwickFixedF.hpp>
      sux::bits::StrideDynRankSel<sux::util::FenwickFixedF, 16> drs(v, n)

    Note that you should subsequently modify the contents of v only through the mutation methods of StrideDynRankSel, or the results will be unpredictable.

    Such a structure is ideal if ranking is the most common operation. If selection is the most common operation a structure based on a byte-compressed level-order tree is faster:

      #include <sux/bits/StrideDynRankSel.hpp>
      #include <sux/util/FenwickByteL.hpp>
      sux::bits::StrideDynRankSel<sux::util::FenwickByteL, 16> drs(v, n);

    In general, by modifying the two template parameters you can use a different stride or a different Fenwick tree structure. A stride is scanned sequentially: the Fenwick tree keeps track of the number of ones appearing at the border of each stride. Structures with single-word strides should be allocated as follows:

      #include <sux/bits/WordDynRankSel.hpp>
      #include <sux/util/FenwickFixedF.hpp>
      sux::bits::WordDynRankSel<sux::util::FenwickFixedF> drs(v, n);

    Note that after the construction you should modify the vector v only by means of the methods of the structure.

  • Similary, if v is a list of n values bounded by 10000 a fixed-size Fenwick tree in classical Fenwick layout can be created by

      #include <sux/util/FenwickFixedF.hpp>
      sux::util::FenwickFixedF<10000> ft(v, n);

    Note that the vector v is only read at construction time, and it is not subsequently accessed by the tree.

    Such a tree is ideal if prefix sums are the most common operations. If find is the most operation, again a byte-compressed level-order structure is faster:

      #include <sux/util/FenwickByteL.hpp>
      sux::util::FenwickByteL<10000> ft(v, n);

    For maximum compression, in particular if the bound is very small, you can use a bit-compressed tree, which however will be a bit slower:

      #include <sux/util/FenwickBitF.hpp>
      sux::util::FenwickBitF<3> ft(v, n);

    Note that v is read at construction time, but it is not referenced afterwards.

  • To create a minimal perfect hash function from a vector of strings keys, with leaf size 8 and bucket size 100, use

      #include <sux/function/RecSplit.hpp>
      sux::function::RecSplit<8> mph(keys, 100)

    It will use abount 1.8 bits per key. Increasing the leaf and bucket sizes gives much more compact structures (1.56 bits per key), at the price of a slower construction time:

      #include <sux/function/RecSplit.hpp>
      sux::function::RecSplit<16> mph(keys, 2000)

    The class sux::function::RecSplit implements the operator sux::function::RecSplit::operator()(const string &key) , so you can obtain the number associated with a string key k with mph(k).

Memory allocation

Almost all data structures make it possible to allocate memory in different ways, and in particular to use transparent large pages (usually, 2MiB) on Linux. All allocations are based on the class sux::util::Vector, which is a zero-cost wrapper around an array (no bound checks), and has a template parameter for choosing the allocation strategy depending on an item of sux::util::AllocType.

For example,

    #include <sux/util/FenwickFixedF.hpp>

    sux::util::FenwickFixedF<10000, MALLOC> f(v, n)

creates a Fenwick tree as above, using a standard malloc() call, which is usually the default, and the most compatible approach, but

    #include <sux/util/FenwickFixedF.hpp>

    sux::util::FenwickFixedF<10000, TRANSHUGEPAGE> f(v, n)

will try to use transparent huge pages instead, if available.


    #include <sux/function/RecSplit.hpp>

    sux::function::RecSplit<8, TRANSHUGEPAGE> rs(keys, 100)

creates a RecSplit instance using transparent huge pages.

If you want to test a static rank/select structure using a certain allocation strategy, it is usually a good idea to allocate both the underlying bit vector and the rank/select structure using the same method. You can use sux::util::Vector to this purpose:

    #include <sux/util/Vector.hpp>
    #include <sux/bits/Rank9.hpp>

    sux::util::Vector<uint64_t, SMALLPAGE> v(1000);
    // Modify v
    sux::bits::Rank9<SMALLPAGE> r(&v, num_bits);

where num_bits is less than 64000. The & operator applied to an instance of sux::util::Vector returns a pointer to its backing array.