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  • Concise: Compressed ’n’ Composable Integer Set

    Word Aligned Hybrid (WAH) bitmap compression

    下面是:Concise: Compressed ’n’ Composable Integer Set

    Figure 2 shows an example of CONCISE-compressed bitmap
    made up of 5 words. Words #0, #3, and #5 are literal words
    where, similarly to WAH, the leftmost bit indicates the block
    type (‘1’), while the remaining bits are used to represent an uncompressed
    31-bit block. Words #1, #2, and #4 are fill words:
    the first (leftmost) bit is the block type (‘0’), the second bit is
    the fill type (a sequence of 0’s or 1’s), the following 5 bits are
    the position of a “flipped” bit within the first 31-bit block of the
    fill, and the remaining 25 bits count the number of 31-blocks
    that compose the fill minus one. When position bits equal 0
    (binary ‘00000’), the word is a “pure” fill, similar to that of
    WAH. Otherwise, position bits indicate the bit to switch (from
    0 to 1 in a sequence of 0’s, or from 1 to 0 in a sequence of 1’s)
    within the first 31-bit block of the sequence represented by the
    fill word. That is, 1 (binary ‘00001’) indicates that we have to
    flip the rightmost bit, while 31 (binary ‘11111’) indicates that
    we have to flip the leftmost one. If we consider bitmaps as a
    representation of integer sets, in Figure 2 Words #2 indicates
    that integers in the range 94–1022 are missing, but 93 is in the
    set since position bits say that the first number of the “missing
    numbers” sequence is an exception.

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  • 原文地址:https://www.cnblogs.com/lpthread/p/4008752.html
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