Unsigned integers

[certik]

All integers in Fortran are signed. It is a common request to include unsigned integers. At the very least to help with the interoperation with the C API that uses unsigned integers.

The best approach currently is to use signed integers of the same size, and then convert them to unsigned Fortran integers of a bigger size appropriately.

[zbeekman]

Yes, for certain algorithms (hash functions) the wrap around nature of unsigned ints is convenient and it would lead to less confusion with C interop. I do not believe the standard requires integers to be implemented as two's complement, but I do not know of a compiler that uses a different convention. This means that the underlying machinery for unsigned integers is already in place. (And that programmers can "roll their own" but this can be confusing or less clear/explicit in the source code.

[certik]

After talking about this with a few members on the committee, it seems most are in agreement that having this in the C interop might be a good idea, but allowing this in the Fortran language itself would do more harm than good (vendors don't like it; it's easy to have all kinds of subtle bugs with unsigned integers such as comparing subtracting etc.).

Python does not have unsigned integers, although NumPy does, and so does Julia.
It is true that it would be useful for hash functions. Numerical computational code does not seem to need them.

I can personally see very good arguments both for and against having this in the language itself.
I am leaning towards against, as it keeps the language smaller and excludes many kinds of possible bugs and warnings.

We can start with the C interop, where it should be easier to get agreement, to see if there is anything that would make sense to propose.

[gronki]

I wanted to chime in and say that one important use case of unsigned integers is handling images. To store a monochrome 8-bit image, one either has to use twice-as-large 16 bit integer or store it as 8 bit unsigned int and deal with wrapping modulo 128 which makes any arithmetic operation impossible. This is true for any binary data, not only images. So I think the issue is not stricly C-interop related.

[FortranFan]

I wanted to chime in and say that one important use case of unsigned integers is handling images. To store a monochrome 8-bit image, one either has to use twice-as-large 16 bit integer or store it as 8 bit unsigned int and deal with wrapping modulo 128 which makes any arithmetic operation impossible. This is true for any binary data, not only images. So I think the issue is not stricly C-interop related.

I agree with this: unsigned integers can be of great help in any systems programming context, handling of binary data of any form (images or otherwise) can be a use case within this space. Though some will argue unsigned integers are not an absolute must for systems programming, the fact is this facility can really make coders' lives easier. If Fortran intends to be taken truly seriously as a general-purpose language, it should consider including unsigned integers; its type system is general and it does not in any way appear to interfere with its introduction.

Interestingly, unsigned integers feature was 4th on the top 6 list of desired features by users in the WG5 survey for Fortran 202X. Ignoring this any longer feels like suppression of the voice of the customers!

[certik]

I just want to react to this particular point:

If Fortran intends to be taken truly seriously as a general-purpose language

Fortran is not a general-purpose language. Rather, it is a domain specific language for array oriented scientific computing.

As a larger point, it touches what we want Fortran to be, see #59.

[gronki]

Fortran is not a general-purpose language. Rather, it is a domain

specific language for array oriented scientific computing. I agree with this and with that direction, however reading/writing binary data is often a part of it, and this is the place where lack of byte/uint really bit me as very often data is stored as uint16 FITS/TIFF files. Dominik pon., 28 paź 2019 o 22:31 Ondřej Čertík <notifications@github.com> napisał(a):

…

I just want to react to this particular point: If Fortran intends to be taken truly seriously as a general-purpose language Fortran is not a general-purpose language. Rather, it is a domain specific language for array oriented scientific computing. As a larger point, it touches what we want Fortran to be, see #59 <#59>. — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#2?email_source=notifications&email_token=AC4NA3N4HGNT7GC7E7BKHMDQQ5K3XA5CNFSM4JBFTXZKYY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGOECOOZEY#issuecomment-547155091>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AC4NA3LG6CZDOIS7GUO7UIDQQ5K3XANCNFSM4JBFTXZA> .

[certik]

@gronki I think you are right about the use case of reading binary data files. Let's collect such use cases. I think we want to be able to write readers and writers for binary files in Fortran.

[FortranFan]

I just want to react to this particular point:

If Fortran intends to be taken truly seriously as a general-purpose language

Fortran is not a general-purpose language. Rather, it is a domain specific language for array oriented scientific computing.
..

That may be the current reality with Fortran, but almost everyone who have worked on its language design and continue to do so will greatly dislike being reduced as such and would very much want Fortran to be seen as a general-purpose language. It's a different matter whether the words are backed up by actions!

[certik]

Let's continue the discussion what Fortran should become here: #59. I started in this comment: #59 (comment).

[klausler]

I'm not sure that Fortran needs an unsigned type so much as it actually needs some unsigned operations and relations. Be wary of simply copying-and-pasting C's unsigned types into Fortran, for they are full of pitfalls that shouldn't be perpetuated, mostly around their interactions with signed types and conversions.