an oldie but a goodie .. ISO C90 does not support 'long long'

[Jakob Bohm]

On 2022-11-06 23:14, raf via openssl-users wrote:
> On Sat, Nov 05, 2022 at 02:22:55PM +0000, Michael Wojcik <Michael.Wojcikatmicrofocus.com> wrote:
>
>>> From: openssl-users <openssl-users-bounces at openssl.org> On Behalf Of raf via
>>> openssl-users
>>> Sent: Friday, 4 November, 2022 18:54
>>>
>>> On Wed, Nov 02, 2022 at 06:29:45PM +0000, Michael Wojcik via openssl-users
>>> <openssl-users at openssl.org> wrote:
>>>
>>>> I'm inclined to agree. While there's an argument for backward compatibility,
>>>> C99 was standardized nearly a quarter of a century ago. OpenSSL 1.x is
>>>> younger than C99. It doesn't seem like an unreasonable requirement.
>>> Would this be a choice between backwards-compatibility with C90
>>> compilers and compatibility with 32-bit architectures?
>> I don't see how.
>>
>> It's a question of the C implementation, not the underlying
>> architecture. A C implementation for a 32-bit system can certainly
>> provide a 64-bit integer type. If that C implementation conforms to
>> C99 or later, it ought to do so using long long and unsigned long
>> long. (I'm excluding C implementations for exotic systems where, for
>> example, CHAR_BIT != 8, such as some DSPs; those aren't going to be
>> viable targets for OpenSSL anyway.)
>>
>>> Is there another way to get 64-bit integers on 32-bit systems?
>> Sure. There's a standard one, which is to include <stdint.h> and
>> use int64_t and uint64_t. That also requires C99 or later and an
>> implementation which provides those types; they're not required.
> Sorry. I assumed that it was clear from context that I was only
> thinking about C90-compliant 64-bit integers on 32-bit systems.
>
>> And for some implementations there are implementation-specific
>> extensions, which by definition are not standard.
>>
>> And you can roll your own. In a non-OO language like C, this would
>> be intrusive for the parts of the source base that rely on a 64-bit
>> integer type.
>>
>>> I suspect that that there are more 32-bit systems than there are
>>> C90 compilers.
>> Perhaps, but I don't think it's relevant here. In any case, OpenSSL is
>> not in the business of supporting every platform and C implementation
>> in existence. There are the platforms supported by the project, and
>> there are contributed platforms which are included in the code base
>> and supported by the community (hopefully), and there are unsupported
>> platforms.
>>
>> If someone wants OpenSSL on an unsupported platform, then it's up to
>> them to do the work.
> So it sounds like C90 is now officially unsupported.
> I got the impression that, before this thread, it was believed
> that C90 was supported, and the suggestion of a pull request
> indicated a willingness to retain/return support for C90.
> Perhaps it just indicated a willingness to accept community
> support for it.
>
> I'd be amazed if anyone could actually still be using a
> 30 year old C90 compiler, rather than a compiler that
> just gives warnings about C90. :-)
>
Regarding C90 compilers, it is important to realize that some system
vendors kept providing (arbitrarily extended) C90 compiler long after
1999.  Microsoft is one example, with many of their system compilers
for "older" OS versions being based on Microsoft's C90 compilers.
  These compilers did not provide a good stdint.h, but might be coached
to load a porter provided stdint.h that maps int64_t and uint64_t to
their vendor specific C90 extensions (named __int64 and unsigned __int64).

Even worse, I seem to recall at least one of those compilers miscompiling
64 bit integer arithmetic, but working acceptably with the older OpenSSL
1.0.x library implementations of stuff like bignums (BN) and various pure
C algorithm implementations in OpenSSL 1.0.x, that happened to do 
everything
by means of 32 and 16 bit types.

As part of our company business is to provide software for the affected
"older" systems, thus desiring the ability to compile OpenSSL 3.x with
options indicating "compiler has no good integral types larger than
uint32_t, floating point is also problematic"

Other major vendors with somewhat old C compilers include a few embedded
platforms such as older ARM and MIPS chips that were mass produced in
vast quantities.

Performance wise, using a newer compiler that implements int64_t etc. via
frequent library calls, while technically correct, is going to run
unnecessarily slow compared to having algorithms that actually use the
optimal integral sizes for the hardware/compiler combination.

I seem to recall using at least one bignum library (not sure if OpenSSL
or not) that could be configured to use uint32_t and uint16_t using the
same C code that combines uint64_t and uint32_t on newer hardware.


Enjoy

Jakob
-- 
Jakob Bohm, CIO, Partner, WiseMo A/S.  https://www.wisemo.com
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