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DACs: Bringing direct access to variable-length codes
(2013)
is ubiquitous in many sorts of appli-
cations, particularly in compressed data structures, but also arises in everyday programming. Using bitmaps aligned to the
codes in order to mark their beginnings is a folklore idea that has been used many times (Fano, 1971...
Grammar compressed sequences with rank/select support
(Elsevier, 2017)
in O (logn) time. This folklore idea, which we call DELTA, has been used repeatedly; see e.g. [33].
5. Grammar-compressed bitmaps
The only bitmap representation we are aware of that exploits repetitiveness in the bitmaps is due to Navarro et al. [47]
PB...
Word-Based Self-Indexes for Natural Language Text
(ASSOC COMPUTING MACHINERY, 2012-02)
, about half a million are negative
values. Albeit not a very large percentage, encoding those values improperly does impact
compression ratios.
When using δ–codes, negative values must be encoded somehow as exceptions. We also
consider another folklore...