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diff --git a/incbwt/bits/nibblevector.h b/incbwt/bits/nibblevector.h
new file mode 100644
index 0000000..c45b425
--- /dev/null
+++ b/incbwt/bits/nibblevector.h
@@ -0,0 +1,148 @@
+#ifndef NIBBLEVECTOR_H
+#define NIBBLEVECTOR_H
+
+#include <fstream>
+
+#include "bitvector.h"
+
+
+namespace CSA
+{
+
+
+/*
+  This class is used to construct a NibbleVector.
+*/
+
+class NibbleEncoder : public VectorEncoder
+{
+  public:
+    NibbleEncoder(usint block_bytes, usint superblock_size = VectorEncoder::SUPERBLOCK_SIZE);
+    ~NibbleEncoder();
+
+    void setBit(usint value);
+    void setRun(usint start, usint len);
+
+    // FIXME for gap encoding
+    inline void nibbleEncode(usint diff, usint len)
+    {
+      this->size += diff + len - 1;
+      this->items += len;
+      this->buffer->writeNibbleCode(diff);
+      this->buffer->writeNibbleCode(len);
+    }
+
+  protected:
+
+    // These are not allowed.
+    NibbleEncoder();
+    NibbleEncoder(const NibbleEncoder&);
+    NibbleEncoder& operator = (const NibbleEncoder&);
+};
+
+
+/*
+  This bit vector uses nibble coding. Each block is either run-length encoded or
+  gap encoded, depending on the first nibble.
+
+  // FIXME reverting to gap encoding not implemented yet
+*/
+
+class NibbleVector : public BitVector
+{
+  public:
+    typedef NibbleEncoder Encoder;
+
+    NibbleVector(std::ifstream& file);
+    NibbleVector(Encoder& encoder, usint universe_size);
+    ~NibbleVector();
+
+//--------------------------------------------------------------------------
+
+    usint reportSize() const;
+
+//--------------------------------------------------------------------------
+
+    class Iterator : public BitVector::Iterator
+    {
+      public:
+        Iterator(const NibbleVector& par);
+        ~Iterator();
+
+        usint rank(usint value, bool at_least = false);
+
+        usint select(usint index);
+        usint selectNext();
+
+        pair_type valueAfter(usint value);
+        pair_type nextValue();
+
+        pair_type selectRun(usint index, usint max_length);
+        pair_type selectNextRun(usint max_length);
+
+        bool isSet(usint value);
+
+        // Counts the number of 1-bit runs.
+        usint countRuns();
+
+        static const usint GAP_ENCODING = 0;
+        static const usint RUN_LENGTH_ENCODING = 1;
+
+      protected:
+
+        // FIXME for gap encoding
+        inline void valueLoop(usint value)
+        {
+          this->getSample(this->sampleForValue(value));
+
+          if(this->val >= value) { return; }
+          while(this->cur < this->block_items)
+          {
+            this->val += this->buffer.readNibbleCode();
+            this->cur++;
+            this->run = this->buffer.readNibbleCode() - 1;
+            if(this->val >= value) { break; }
+
+            this->cur += this->run;
+            this->val += this->run;
+            if(this->val >= value)
+            {
+              this->run = this->val - value;
+              this->val = value;
+              this->cur -= this->run;
+              break;
+            }
+            this->run = 0;
+          }
+        }
+
+        inline void getSample(usint sample_number)
+        {
+          BitVector::Iterator::getSample(sample_number);
+          this->run = 0;
+//           this->use_rle = this->buffer.readNibble();
+        }
+
+        bool use_rle;
+
+        // These are not allowed.
+        Iterator();
+        Iterator(const Iterator&);
+        Iterator& operator = (const Iterator&);
+    };
+
+//--------------------------------------------------------------------------
+
+  protected:
+
+    // These are not allowed.
+    NibbleVector();
+    NibbleVector(const NibbleVector&);
+    NibbleVector& operator = (const NibbleVector&);
+};
+
+
+} // namespace CSA
+
+
+#endif // NIBBLEVECTOR_H