在 Javascript 和 C++ 中计算 MD5 哈希的不同结果

Question

I am trying to calculate an MD5 hash for a certain value in Javascript and in C++ but the different programming languages are giving different outputs at times. As it does not happen constantly I am guessing it has something to do with rounding errors.

In Javascript I am calculating the value as follows:

let calculatedTotal = 0;
blocks.forEach((block) => {
   calculatedTotal += Math.floor(block.standard_deviation * 1000);
});

In C++ using rapidJson I am doing:

for (rapidjson::Value::ConstValueIterator j = blocks.Begin(); j != blocks.End(); ++j) {
    float val = (*j)["standard_deviation"].GetFloat();
    sumToCalculteHashOver += int(std::floor(val * 1000));
}

As shown in C++ I am using a float.

Does anyone know what could be the cause of this?

Answer 1

I managed to solve this thanks to @Caramiriel.

The issue has, as I kinda expected, to do with the precision of floating point numbers in C++.

Using an integer value in my calculations worked. For me that meant I needed to make these changes.

Javascript:

let calculatedTotal = 0;
blocks.forEach((block) => {
   calculatedTotal += Math.floor(block.standard_deviation) * 1000;
});

C++:

for (rapidjson::Value::ConstValueIterator j = blocks.Begin(); j != blocks.End(); ++j) {
    int val = int(std::floor((*j)["standard_deviation"].GetFloat()));
    sumToCalculteHashOver += int(std::floor(val * 1000));
}