updated branches to HEAD

[webpac] / doc / exact_match.txt

diff --git a/doc/exact_match.txt b/doc/exact_match.txt
index d749552..2dbb277 100644 (file)
--- a/doc/exact_match.txt
+++ b/doc/exact_match.txt
@@ -27,3 +27,30 @@ on TitleAndResponsibility, you would use:
 <input type="text" name="v1">
 <input type="hidden" name="e1" value="5">
 
+
+What are bit-masks?
+
+Bit-mask is usage of one byte (8 bits) as 8 separate bits with it's own
+meaning (this is simplification, but bear with me for now).
+
+So, 1 = 2^0, thus it's bit 1. With analogy, 2=2^1 and 3=2^0+2^1. 
+So, for 1-3 we use two bits and have:
+
+number bits
+1      01      (just begin bit set)
+2      10      (just end bit set)
+3      11      (begin and end bit set)
+
+Thus, with two bits (and values 1-3) we can express should we exact match from
+beginning, end or both. For wild-card match, we use additional bit 3 (2^3 = 4)
+so we have:
+
+number bits    exact match
+1      001     begin
+2      010     end
+3      011     begin+end
+4      100     (not used)
+5      101     (4+1) begin+wild-card
+6      110     (4+2) end+wild-card
+7      111     (4+3) begin+end+wild-card
+