[OpenSIPS-Devel] [opensips] math_eval() does not handle negative numbers (#788)

[rrb3942]

I understand what your saying, but coming at this from the stance of a user I think it is a problem since it can greatly complicate an algorithm if you cannot pass in a negative number.

It is also a problem when you can't feed the output of math_eval back into itself, especially since at the script level these are stored as strings, which can't be converted to an int to check their sign. This is a problem if you would like to keep an intermediate result around, and generally just unintuitive. 

        math_eval("5-7","$var(temp)");
        //outputs 'Temp is : -2.000000'
        xlog("Temp is : $var(temp)");

        //Fails with 'cannot get left var value'
       //Fails without transformation as well but instead receives 'invalid LESS_THAN operation: left is          NONE/STRING_VAL, right is NUMBER/NO_VAL'
        if ($(var(temp){s.int}) < 0) {
                xlog("$var(temp) is negative");
        }

       //Will fail because $var(temp) is negative
        math_eval("$var(temp) + 9", "$var(temp2)");

I suppose you could do a substr to get the first character and check that way, but now we are doing string operations to deal with a math problem and we have to check the sign after every subtraction. Unless you are going to remove support for subtraction, negative numbers should really be handled.

What are you thoughts on using something like TinyExpr from https://github.com/codeplea/tinyexpr ?

It seems to handle the above cases well and even opens up for using standard C math functions in the expression as well. It also has test coverage, so it should handle potential corner cases better. It is zlib licensed, which I think is compatible? And it should be pretty easy to include.

If you think that looks like a reasonable solution I don't mind writing up a patch to convert the math_eval() function to use it.

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Reply to this email directly or view it on GitHub:
https://github.com/OpenSIPS/opensips/issues/788#issuecomment-184394774
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