I'm finishing up an implementation of the 6.3.0 Bidi algorithm and hit a snag:
currently passing all tests but one.
After much careful re-re-reading of the spec, I can't quite figure out where
this thing is going wrong and would really appreciate some advice, or perhaps
someone who knows that this test case is in fact incorrect (unlikely as that
may be).
The particular test case is this:
0661 0009 0028 0662 0029;2;0;2 0 1 2 1;0 1 4 3 2
(line 184 of BidiCharacterTest.txt)
The "correct" levels are [2 0 1 2 1], however, this implementation resolved the
levels to be [2 1 1 2 1]. A single incorrect level for the Segment Separator at
index 1.
Below is a trace of the algorithm (apologies if this is not visible on your end
in a monospaced font, it is much more readable that way). In stage [N1] the S
at index 1 becomes R. This seems correct to me because the previous character
at index 0 is AN (interpreted as R according to the spec) and the following
character at index 2 is an R. Both preceding and following characters are the
same direction, so the S becomes an R as well.
At stage [Resolving_Implicit_Levels], the R (previously S) at index 1 has an
even level (0), so its level is increased by one (0->1). I'm not entirely sure
why the test has the level staying at 0, unless I missed something else
completely unrelated to these two stages mentioned.
Any advice would be greatly appreciated, thanks very much!
Loren
---
TRACE:
[Initializaton+The_Paragraph_Level]
pe: 0
index: 0 1 2 3 4
character: 0661 0009 0028 0662 0029
matching: - - - - -
bidiclass: AN S ON AN ON
embedding: 0 0 0 0 0
[Explicit_Levels_and_Directions]
matching: - - - - -
bidiclass: AN S ON AN ON
embedding: 0 0 0 0 0
[Preparations_for_Implicit_Processing]
matching: - - - - -
bidiclass: AN S ON AN ON
embedding: 0 0 0 0 0
[Resolving_Weak_Types]
matching: - - - - -
bidiclass: AN S ON AN ON
embedding: 0 0 0 0 0
[N0]
matching: - - 4 - -
bidiclass: AN S R AN R
embedding: 0 0 0 0 0
[N1]
matching: - - 4 - -
bidiclass: AN R R AN R
embedding: 0 0 0 0 0
[N2]
matching: - - 4 - -
bidiclass: AN R R AN R
embedding: 0 0 0 0 0
[Resolving_Neutral_and_Isolate_Formatting_Types]
matching: - - 4 - -
bidiclass: AN R R AN R
embedding: 0 0 0 0 0
[Resolving_Implicit_Levels]
matching: - - 4 - -
bidiclass: AN R R AN R
embedding: 2 1 1 2 1
