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  1. Terrier Core
  2. TR-337

Elias delta coding not working

          Details

          • Type: Bug
          • Status: Resolved
          • Priority: Trivial
          • Resolution: Fixed
          • Affects Version/s: 4.0
          • Fix Version/s: 4.1
          • Component/s: .compression
          • Labels:
            None

            Description

            The Elias delta coding implemented in BitOutputStream.java/BitInBase.java does not seem to work properly in cases where the rest (unary, gamma and a fixed version of Golomb) work fine. For instance when X = 3309, the coding/decoding process results in X'=6618. I've tried to debug it, but I don't understand exactly what is happening. It looks like a problem when retrieving the gamma representation of the msb, but I cannot see why.

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                saulvargas Saúl Vargas added a comment -

                FIXED! See the original, commented line and the next one with the fix. Don't forget to fix it in BitOutputStream.java and BitFile.java (duplicated code, WHY?).

                /**

                {@inheritDoc}

                **/
                public int writeDelta( int x ) throws IOException

                { final int msb = BitUtilities.mostSignificantBit( ++x ); final int l = writeGamma( msb ); // return l + ( msb != 0 ? writeInt( x, msb ) : 0 ); return l + ( msb != 0 ? writeInt( x & ((2 << (msb - 1)) - 1), msb ) : 0 ); }
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                saulvargas Saúl Vargas added a comment - FIXED! See the original, commented line and the next one with the fix. Don't forget to fix it in BitOutputStream.java and BitFile.java (duplicated code, WHY?). /** {@inheritDoc} **/ public int writeDelta( int x ) throws IOException { final int msb = BitUtilities.mostSignificantBit( ++x ); final int l = writeGamma( msb ); // return l + ( msb != 0 ? writeInt( x, msb ) : 0 ); return l + ( msb != 0 ? writeInt( x & ((2 << (msb - 1)) - 1), msb ) : 0 ); }
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                saulvargas Saúl Vargas added a comment -

                ...and the corresponding test.

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                saulvargas Saúl Vargas added a comment - ...and the corresponding test.
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                craigm Craig Macdonald added a comment -

                Fixed for 4.1

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                craigm Craig Macdonald added a comment - Fixed for 4.1

                  People

                  • Assignee:
                    craigm Craig Macdonald
                    Reporter:
                    saulvargas Saúl Vargas
                  • Watchers:
                    0 Start watching this issue

                    Dates

                    • Created:
                      Updated:
                      Resolved: