Question

Below is the code in C++,

Num *= other.Den;
Den *= other.Num;
if (Den.isNegative()) {
    Num = -Num;
    Den = -Den;
}
assert(Den.isStrictlyPositive());

where Num and Den are of type LLVM::APInt.

For some reason I am getting the assertion failed. I have checked if the Denominator is negative explicitly and turned it positive. Can someone please let me in what scenario in this code, the assertion can fail? When I run my code against test case it fails. The test case is very large, and I have not been successful in cornering a particular case. The above code is a part of my algorithm which is doing some other job.

Here is the implementation of isStrictlyPositive. It is using the LLVM library file APInt.h.

bool isStrictlyPositive() const {
return isNonNegative() && !!*this;
}

bool isNonNegative() const {
return !isNegative();
}

Answer 1

I’m basing this off the following assumptions:

• Strictly positive means > 0
• isNegative is < 0

Given the snippet you quoted, the function isStrictlyPositive boils down to:

return isNonNegative() && !!*this;

Which is equivalent to:

return !(*this < 0) && !!*this;

!!*this is equivalent to !(!*this) which is equivalent to !(*this==0) which is equivalent to *this!=0, so the expression is:

return !(*this < 0) && *this!=0;

Which can be simplified to:

return *this>=0 && *this!=0;

Which is really just:

return *this > 0;

So, your issue is that Den is 0 and is therefore not negative and not strictly positive.