Expression parser support for order of operations and unary negation operator

[sMezaOrellana]

I realized that the expression parser class was not able to parse more 'complex' expressions.
Things like "4 * 1 + 1" would not equal "5". The previous expression parser did not support the order of operations.
I implemented this using a shunting yard parsing algorithm[1] for evaluating arithmetic expressions. I also added support for unary operators like '-' and '~'.
This implementation mostly follows the order of precedence defined in the C standard[2]. I added some more tests.

Fan of this project.

[1]
https://en.wikipedia.org/wiki/Shunting_yard_algorithm
[2]
https://en.cppreference.com/w/c/language/operator_precedence

[Schamper]

Thanks for the amazing PR! I'm unfortunately personally out of office for another week but I've assigned @pyrco to review it. You should also receive a contributor agreement message shortly as a reply on this PR (our bot is unfortunately still a human and out of office too ;))

One quick question I already have: is it possible to support integer suffixes with your parser (#32)?

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[sMezaOrellana]

@DissectBot agree []

[sMezaOrellana]

One quick question I already have: is it possible to support integer suffixes with your parser (#32)?

Yes this could be supported by slightly modifying the tokenizer. I will look at it

[sMezaOrellana]

I have added support for suffixes. This means that when we encounter a number like '10ull' this gets parsed into '10'.
Suffixes are parsed according to [1] This means a number can have the following suffixes u, l, ll, ul, ull, lu, llu either in uppercase or lowercase. There are some edge cases to consider. If we look at the specifications [2]:

 std::cout << -9223372036854775808u << '\n'; // unary minus applied to unsigned
                // value subtracts it from 2^64, this evaluates as 9223372036854775808

The upper code would output 9223372036854775808 however because of how Python works we output:
-9223372036854775808
[1]
https://www.ibm.com/docs/de/zos/2.1.0?topic=literals-integer

[2]
https://en.cppreference.com/w/cpp/language/integer_literal

[sMezaOrellana]

Hi I see that the changes were just added. I was busy rounding up some uni work the past few weeks. Glad that this still found a place in the project.

[Schamper]

Hi I see that the changes were just added. I was busy rounding up some uni work the past few weeks. Glad that this still found a place in the project.

No worries, I understand! I'd very much like this to be a part of the project so I found some free time to make my suggested changes myself.

[codecov]

Codecov Report

Merging #37 (2fff05a) into main (c254806) will increase coverage by 0.74%.
The diff coverage is 98.32%.

@@            Coverage Diff             @@
##             main      #37      +/-   ##
==========================================
+ Coverage   88.23%   88.98%   +0.74%     
==========================================
  Files          20       20              
  Lines        1709     1852     +143     
==========================================
+ Hits         1508     1648     +140     
- Misses        201      204       +3     

Flag	Coverage Δ
unittests	88.98% <98.32%> (+0.74%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
dissect/cstruct/expression.py	97.28% <98.28%> (+1.72%)	⬆️
dissect/cstruct/exceptions.py	100.00% <100.00%> (ø)

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[Schamper]

@sMezaOrellana again, huge thanks for this PR!