3.1.8.1.5.1 Zero Run-Length Encoding

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Runs of zeros are encoded using the same techniques as RLGR. The KP state value defines the likelihood of encountering long runs of zeros.

  • The initial value of KP is 8.

  • K is defined as KP / 8 (rounded down) and indicates the number of bits that MUST be used to encode the number of zeros (nz).

  • If nz >= (1 << K) then:

    • One "0" bit is written

    • nz = nz - (1 << K)

    • KP = KP + 4; if KP > 80 then KP = 80

    • K = KP / 8

    • Repeat until nz < (1 << K)

  • Otherwise,

    • One "1" bit is written

    • The count of zeros is written using K bits

    • KP = KP - 6; if KP < 0 then KP = 0

    • K = KP / 8

Note that, contrary to RLGR, it is possible to encode a run of zeros with K = 0. If the length of the run is zero, a single "1" bit is written.