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# Diff of /branches/ffzg/doc/exact_match.txt

revision 289 by dpavlin, Sun Mar 14 20:08:29 2004 UTC revision 303 by dpavlin, Sun Apr 4 22:11:13 2004 UTC
# Line 27  on TitleAndResponsibility, you would use Line 27  on TitleAndResponsibility, you would use
27  <input type="text" name="v1">  <input type="text" name="v1">
28  <input type="hidden" name="e1" value="5">  <input type="hidden" name="e1" value="5">
29
30
31    What are bit-masks?
32
33    Bit-mask is usage of one byte (8 bits) as 8 separate bits with it's own
34    meaning (this is simplification, but bear with me for now).
35
36    So, 1 = 2^0, thus it's bit 1. With analogy, 2=2^1 and 3=2^0+2^1.
37    So, for 1-3 we use two bits and have:
38
39    number  bits
40    1       01      (just begin bit set)
41    2       10      (just end bit set)
42    3       11      (begin and end bit set)
43
44    Thus, with two bits (and values 1-3) we can express should we exact match from
45    beginning, end or both. For wild-card match, we use additional bit 3 (2^3 = 4)
46    so we have:
47
48    number  bits    exact match
49    1       001     begin
50    2       010     end
51    3       011     begin+end
52    4       100     (not used)
53    5       101     (4+1) begin+wild-card
54    6       110     (4+2) end+wild-card
55    7       111     (4+3) begin+end+wild-card
56

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