What is the opinion of matlabs "extra rounding improvements"?

Hi, during my work with matlab I have noticed that matlab always tries to improve some basic functionality of other programming languages. Some examples.

a = cast(0.5,'int32') % a = 1
a = cast(-1.5,'uint32') % a = 0
a = int32(1)/int32(2) % a = 1

The division can of course be solved by idivide, but the issues with cast remains. Also this definitely shows that matlab cannot properly do integer operations since the decimals are obviously used by the /.

Is there some way to do a cast that works as it should in matlab? What is the general opinion of matlabs " IMPROVED " behaviour?

Answer 1

[Walter Roberson]

MATLAB uses "saturation" arithmetic when converting to the integer data types. Any value that is larger than the integer type can hold is converted to the largest value that can be held, and any value that is less than the integer type can hold is converted into the smallest value that can be held. As the smallest value that unsigned integer types can hold is 0, negative values get transformed into 0.

If you examine the behavior of other languages such as C, you will find that casting a signed value into an unsigned integer does depend upon sign. If you do not want it to, then take abs() before doing the type conversion.

Whether integer operations round or truncate does not matter much to me; in cases where it matters, I can document and (if needed) I can code around it.

[Patrik Ek]

Thanks for the answer. This was kind of what a I was asking.

Answer 2

[John D'Errico]

"a = cast(-1.5,'unit32') % a = 0"

So is unit32 a new data type? Maybe a 32 bit scalar, that always takes on the value 1?

I'll assume you simply cannot type, and really meant uint32. Of course, then you did not actually bother to test the code you posted, a no-no.

Are you seriously surprised that when you cast a negative number to a non-negative integer class, that you got zero??????? You think this is a bad thing? What did you expect to get out here? pi?

As far as "improving" functionality, there is no claim to an improvement, merely a behavior that is its own. You learn how a language works. Every language will generally be subtly different, with its own characteristic behavior based on decisions made by those who designed the language. Clearly you disagree with those decisions, while I don't care, as I am not closely wedded to some other language. As far as I can see, once you fully learn to use a tool, you learn its characteristic behavior, and there are no problems. One can always get the answer needed, as long as one knows what to expect.

Sorry for a response that may appear a bit sarcastic, but your question is really more of a rant than a question. When you make claims that MATLAB ALWAYS does something, you are making broad assertions that will not be accurate for any tool as large as MATLAB, and are clearly intended as flame bait. Likewise, you ask for the general opinion of people, when you have made your opinion very clear on the matter.

[Patrik Ek]

Sorry typo it should be 'uint32'. However, thanks for your opinion. However imo, cast of a uint should not bother about sign. It is called unsigned integer for a reason. Also the ceil and floor is also existing for a reason and casting an int should really truncate, so to say, only take the integer part. Rounding in cast, together with integer division that really is no real integer division, since it still uses decimals is potentially disastrous together. But take no offense of this. I only asked for your opinion and is glad that you expressed it. I am mostly interested to learn if there are some way that is fairly simple and do not need extra functions as floor or ceil for simulating an ignoration of decimals. Also I am a bit curious about what people have to say about this. A programming language is about clarity as well and calling something uint, but still regard the decimal does not give the expected output.

[Patrik Ek]

Well I see your point, should I remove the question?

[Walter Roberson]

I suggest leaving it as it might be of interest to others.