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Hi Everyone, We have three last days remaining for safe_numerics review (till March 11th). If you like working under time pressure, this is the perfect moment for doing your review.

If you would like to submit your review, but feel you will not make it till March 11th, let me know, we can try to extend the review period.

FWIW, I feel that this is a complex library and people clearly need more time to consider it.

For me personally, this is a library really far from my experience. I've never used anything like it before. It looks fine, the design looks good, implementation the same and the docs reasonable. But I'm also aware there are alternatives out there in the open source and I don't know how this compares to those. I also know proposals about this domain have gone before WG21 in the past, and I don't know how those compare to this either. This is why I, and I suspect many others, haven't given a review nor intend to. I have such low confidence in my opinion of this library that I feel it worthless to say anything about it all other than "it looks okay". Hence extending the review period I suspect will make little difference. Niall -- ned Productions Limited Consulting http://www.nedproductions.biz/ http://ie.linkedin.com/in/nialldouglas/

2017-03-10 16:00 GMT+01:00 Robert Ramey via Boost :

On 3/10/17 5:16 AM, John Maddock via Boost wrote:

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On 10/03/2017 08:24, Andrzej Krzemienski via Boost wrote:

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Hi Everyone, We have three last days remaining for safe_numerics review (till March 11th). If you like working under time pressure, this is the perfect moment for doing your review.

If you would like to submit your review, but feel you will not make it till March 11th, let me know, we can try to extend the review period.

I'm going to try and write a review, but as well as being short on time, I'm hitting a lot of issues, most notably at present that almost all the tests include cxxabi.h which is a GCC libstdc++ internal header, is there a reason for this?

Hmm - I just looked into this. Most of them are superfluous. I built and tested with CLang and GCC. I wasn't able to get appveyor to work to test on VC. That's why I didn't pick this up sooner.

Is it possible to apply a quick fix, to unblock John? Regards, &rzej;

I'm very, very concerned that there are only a very few reviews (actually really just one !!!). In the past I've railed against the acceptance of libraries with only two reviews !!! I don't really know what else to say about this. I'll just punt to the review manager.

I think the problem is this: normally we review largely based on interface and the design - get the design right and the internals usually take care of themselves. However, in this case the design is (hopefully) exceptionally uncontroversial - it looks like an int, smalls like an int, and behaves like an int. There really isn't much to get your teeth into there. What really matters is that: * It's functionally correct. * It truly is a drop in replacement for type int, with no nasty surprises. * It's performance compared to int isn't so dreadful that no one uses it. Unfortunately reviewing these points requires some exceptionally detailed work: the internals of the library are sufficiently complex, and use enough unfamiliar (to me at least) C++14 features, that this is not an easy task. I confess at present to be deeply surprised at how complex the internals are... Best, John. --- This email has been checked for viruses by AVG. http://www.avg.com

Update: I now have a version which builds and runs all the tests with VC2017, the fixes required are here: https://github.com/robertramey/safe_numerics/pull/33 Hopefully this will encourage a few other people to give this a try. The one exception is test_cast.cpp which triggers the MSVC runtime checks due to the use of an unitialized variable in the test suite, which should obviously be fixed. I also noticed that test_z.cpp has no content: it's all #if'ed out.

Perhaps you might take a different tack. I've spent a little time looking at the boost multi-precision library with the eye of incorporating it into the safe numerics testing. In the course of doing this a couple of interesting things occurred to me.

a) would safe numeric types inter-operate with safe numerics types? They should - but I haven't actually tested this. Whenever I fail to test something - there's almost always a bug in it.

b) would safe<T> work if T is one of the types defined by boost multi-precision? This is unclear to me. safe numerics presumes that the largest types available are std::uintmax_t and std::intmax_t . It's easy to imagine altering this presumption to use types defined by the user to be types like boost::uint512_t or... . I think this would work with minor changes - such a combination would open up whole new territory.

There is overlap between the two libraries here: class cpp_int already has built-in overflow checking that allows it to operate as a checked integer type already. The issue here, is that a generic test for possible overflow is likely to be ruinously expensive compared to built-in support - in fact built in support has basically zero cost since the presence of overflow is already right there in the multiprecision-algorithm, as in "we have more bits in the result but no where left to put them". One thing I want to at least try and do, is figure out whether your extension-API's are suitable for hooking into this along with assembly code overflow checks for native types.

Maybe if you confined the scope of your review to issues such as the above you could save a lot of time and bring up issues that others are not in a position to do.

Finally, my biggest disappointment in all this has been my inability to get people to take this whole effort seriously. That is, to even admit that there is even a problem. It's inexplicable and disheartening to me that one can write something like x + y and not be confident that the result actually equals x + y. Especially in light of the fact that we're using C++ to make flying cars - not just websites. I feel that for the first time in 60 years we're in the position of making demonstrably correct software - and no one cares. It's very frustrating.

I so much appreciate the interaction I have with my Boost soulmates. I'm not sure what I would do with this.

Build it and they will come ;) Best, John. --- This email has been checked for viruses by AVG. http://www.avg.com

AMDG On 03/10/2017 12:25 PM, John Maddock via Boost wrote:

Update: I now have a version which builds and runs all the tests with VC2017, the fixes required are here: https://github.com/robertramey/safe_numerics/pull/33

It's a bit more complex than it needs to be: - msvc_max isn't needed. msvc accepts max(x, y). - boost::core::demangle does all the #ifdef'ing for you. In Christ, Steven Watanabe

2017-03-10 19:56 GMT+01:00 Robert Ramey via Boost :

On 3/10/17 9:22 AM, John Maddock via Boost wrote:

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I'm very, very concerned that there are only a very few reviews

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(actually really just one !!!). In the past I've railed against the acceptance of libraries with only two reviews !!! I don't really know what else to say about this. I'll just punt to the review manager.

I think the problem is this: normally we review largely based on interface and the design - get the design right and the internals usually take care of themselves. However, in this case the design is (hopefully) exceptionally uncontroversial - it looks like an int, smalls like an int, and behaves like an int. There really isn't much to get your teeth into there. What really matters is that:

* It's functionally correct. * It truly is a drop in replacement for type int, with no nasty surprises. * It's performance compared to int isn't so dreadful that no one uses it.

Unfortunately reviewing these points requires some exceptionally detailed work: the internals of the library are sufficiently complex, and use enough unfamiliar (to me at least) C++14 features, that this is not an easy task.

This is a very believable explanation.

I confess at present to be deeply surprised at how

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complex the internals are...

If it makes any difference - it started out a lot simpler. Then it became apparent that the issue of performance could not be ignored in the real world. This meant detecting and filtering out redundant checking. On which I was stuck - until C++14 generalized constexpr which permitted implementation of compile time integer arithmetic. (which actually could/should be a separate library. This in turned motivated the checked integer routines to be constexpr. My interest and concerns for embedded systems and compile time usage of checked integer operations introduced constexpr check_result - basically a kind of monad one can use a compile time. All in all it's the composition of several libraries each of which could/should be a separate boost library. check_result, checked integer arithmetic, integer interval arithmetic. At the top is a layer which defines a safe_integer type and uses enable_if to overload all the binary and unary operations involving safe integers. The implementation of this last would be more concise using concepts-lite in C++20 or Paul Fultz's tick library. But neither of these are in boost or yet in the standard. All of the above is implemented via constexpr where possible.

So as one can see it's actually pretty simple.

It's only now that I've "finished" it, that I see how simple it is.

Steven's exhaustive line by line review of the code is going to be a very tough act follow. This appeared the second day of the review. Maybe that intimated people - it would me. He's pointed out errors which I've agreed to fix. so it's not clear that repeating this process, though it woudn't hurt, might be somewhat redundant.

Perhaps you might take a different tack. I've spent a little time looking at the boost multi-precision library with the eye of incorporating it into the safe numerics testing. In the course of doing this a couple of interesting things occurred to me.

a) would safe numeric types inter-operate with safe numerics types? They should - but I haven't actually tested this. Whenever I fail to test something - there's almost always a bug in it.

b) would safe<T> work if T is one of the types defined by boost multi-precision? This is unclear to me. safe numerics presumes that the largest types available are std::uintmax_t and std::intmax_t . It's easy to imagine altering this presumption to use types defined by the user to be types like boost::uint512_t or... . I think this would work with minor changes - such a combination would open up whole new territory.

FWIW, this is something different, but I tested safe<T> with boost::rational, and at least a simple example works as expected: https://github.com/robertramey/safe_numerics/issues/34 Maybe it is worht adding in tests, examples, docs.

Maybe if you confined the scope of your review to issues such as the above you could save a lot of time and bring up issues that others are not in a position to do.

Finally, my biggest disappointment in all this has been my inability to get people to take this whole effort seriously. That is, to even admit that there is even a problem. It's inexplicable and disheartening to me that one can write something like x + y and not be confident that the result actually equals x + y. Especially in light of the fact that we're using C++ to make flying cars - not just websites. I feel that for the first time in 60 years we're in the position of making demonstrably correct software - and no one cares. It's very frustrating.

Maybe this is advertised incorrectly, or maybe there is a confusion about the expectations from this library. If one sees `safe<int>` one might think, "with this library using ints will be safer". But what does this mean? 1. I can use this library to *test* if my operations overflow? -- yes, it can do that 2. I can use it like asserts: redefine its semantics in "Debug" and "Release" builds, by swapping the policies. -- yes, it can do it; but does documentation say about it? 3. When I use this library, I no longer have to care about overflow bugs, because the library will take care for them for me (like with GC and memory management)? -- no, but is library clear about this? 4. When I use this library, I will never have an overflow again? -- no, but will the users understand that when getting in touch with your library? 5. Whan I use this library, I no longer have to check if I am dividing by zero? -- ok, the library will do th check, but that would actually reduce the quality, if you do not check for this yourself. There exists a trend where a piece of software is considered "safe" or "correct" only because every function has an artificially widened contract and does an if-statement up front and throws an exception if its (hidden) narrow cotract is violated. Does your library take or promote this approach or not? -- One cannot immediately see the answer from the documentation. Regards, &rzej;

Le 10/03/2017 à 18:22, John Maddock via Boost a écrit :

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I'm very, very concerned that there are only a very few reviews (actually really just one !!!). In the past I've railed against the acceptance of libraries with only two reviews !!! I don't really know what else to say about this. I'll just punt to the review manager.

I think the problem is this: normally we review largely based on interface and the design - get the design right and the internals usually take care of themselves. However, in this case the design is (hopefully) exceptionally uncontroversial - it looks like an int, smalls like an int, and behaves like an int. There really isn't much to get your teeth into there. What really matters is that:

* It's functionally correct. * It truly is a drop in replacement for type int, with no nasty surprises. * It's performance compared to int isn't so dreadful that no one uses it.

There is one major difference between int and safe<int>. While int operation don't throw and are seen as noexcept, safe<int> operations can throw and can not be declared as noexcept. It would be different if the policies were required to be noexcept, but I know that a lot of people wants to be able to throw exceptions. From my side, I prefer to assert in this cases. Best, Vicente