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diff --git a/BSGAP.h b/BSGAP.h
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+++ b/BSGAP.h
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+/**
+ * Binary-searchable gap encoding scheme (BSGAP)
+ * Niko Välimäki
+ *
+ * Based on:
+ *
+ * Ankur Gupta and Wing-Kai Hon and Rahul Shah and Jeffrey Scott Vitter. Compressed data structures:
+ * Dictionaries and data-aware measures, Theor. Comput. Sci., Volume 387, Issue 3 (November 2007).
+ */
+#ifndef _BSGAP_H_
+#define _BSGAP_H_
+
+#include "Tools.h"
+#include "BlockArray.h"
+
+class BSGAP
+{
+public:
+    BSGAP(ulong *, ulong, bool = false, ulong = 0);
+    BSGAP(FILE *);
+    ~BSGAP();
+    ulong rank(ulong);
+    ulong rank0(ulong);
+    ulong rank(bool b, ulong i) {return b?rank(i):i+1-rank(i);};
+    ulong select(ulong);
+    ulong select0(ulong);
+    ulong select(bool b, ulong i) {return b?select(i):select0(i);};
+    
+    bool IsBitSet(ulong pos);
+    // Returns also the rank_1(pos) via the second param
+    bool IsBitSet(ulong pos, ulong *);
+    
+    ulong size() {return u;};
+    ulong bitsSet() {return n;}
+    void Save(FILE *) const;
+private:
+    static const uchar bit_table[];
+    ulong u, n;             // Universe size, number of 1-bits in B
+    ulong topCount;   // Top structure and the number of substructures
+    ulong bitsInP;          // Length of bit vector P
+    ulong *P;               // Pointer to BSGAP structures
+    unsigned b;             // Subdictionary size (\log^2 n)
+    BlockArray *offsetA;    // Array of pointers (into bitvector P)
+    BlockArray *firstKeyA;  // Array of first key positions of the substructures
+    
+    ulong rank(ulong *, ulong, ulong, ulong, ulong, ulong, ulong, bool);
+    bool IsBitSet(ulong *, ulong, ulong, ulong, ulong, ulong, ulong, bool);
+    bool IsBitSet(ulong *, ulong, ulong, ulong, ulong, ulong, ulong, bool, ulong *);
+    ulong select(ulong *, ulong, ulong, ulong, ulong, ulong, ulong, bool);
+    ulong select0(ulong *, ulong, ulong, ulong, ulong, ulong, ulong, bool);
+    ulong * GetSubtree(ulong *, ulong, ulong, ulong, ulong, bool, ulong &);
+    ulong DeltaDecode(ulong *, ulong &);
+    ulong DeltaDecode(ulong *, ulong &, bool &);
+    ulong * DeltaEncode(ulong, ulong &, bool = true, bool = false);
+    void BitCopy(ulong *, ulong *, ulong, ulong);
+    ulong FindMedian(ulong *, ulong, ulong, ulong, ulong);
+    unsigned FindLowestBit(ulong);
+
+    inline bool IsSubtreeFull(ulong firstKey, ulong l, ulong r, ulong n)
+    {
+        if (l == firstKey)
+            n --;
+        
+        if (r - l - 1 == n)
+            return true;
+        return false;
+    }
+    /**
+     * Returns the number of zeros in the left subtree
+     */
+    inline ulong numberOfZeros(ulong firstKey, ulong l, ulong key, ulong n)
+    {
+        ulong z = key - l - 1 - n/2;
+        if (l == firstKey)
+            ++z;
+        if (z == -1lu)
+            z = 0;
+        return z;
+    }
+
+    inline ulong FindRightSubtree(ulong *B, ulong offset, ulong firstKey, ulong key, ulong l, ulong r, ulong n)
+    {
+        if (n - n/2 - 1 == 0)
+            return 0;       // Does not exists
+    
+        if (IsSubtreeFull(firstKey, key, r, n - n/2 - 1))
+            return 0;       // Right subtree is full (does not exists)
+    
+        if (n/2 == 0)
+            return offset; // Left subtree does not exists
+    
+        if (IsSubtreeFull(firstKey, l, key, n/2))
+            return offset; // Left subtree is full (does not exists)
+    
+        ulong len = DeltaDecode(B, offset);
+        return offset + len;         // Skipping left subtree
+    }
+
+    inline ulong FindLeftSubtree(ulong *B, ulong offset, ulong firstKey, ulong key, ulong l, ulong r, ulong n)
+    {
+        if (n/2 == 0)
+            return 0;       // Does not exists
+    
+        if (IsSubtreeFull(firstKey, l, key, n/2))
+            return 0;       // Left subtree is full
+    
+        if (n - n/2 - 1 == 0)
+            return offset; // Right subtree does not exists
+    
+        if (IsSubtreeFull(firstKey, key, r, n - n/2 - 1))
+            return offset; // Right subtree is full
+    
+        DeltaDecode(B, offset); // Calculate new offset
+        return offset;      // Left subtree is the first one
+    }
+    
+};
+
+#endif