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Subject: Re: [boost] a safe integer library
From: Robert Ramey (ramey_at_[hidden])
Date: 2015-12-10 14:18:30

On 12/10/15 10:47 AM, John Maddock wrote:

> In:
> "Performance will depend on the implementation and subject to the
> constraints above. This design will permit the usage of template
> meta-programming to eliminate runtime performance penalties in some
> cases. In the following example, there is no runtime penalty required to
> guarantee that incorrect results will never be generated."
> The example that follows surely can overflow:
> void f(safe<int8_t> i){
> safe<int8_t> j;
> j = i * i; // C++ promotion rules make overflow impossible!
> std::cout << j;
> }
> OK so the temporary returned by i*i *may* not overflow (depending on the
> size of type int), but the assignment to j most certainly can

correct, I'll fix this example

  - I would expect that to throw,

it will

> and if not it drives a coach and horses right through the proposal IMO.

agreed. All binary operators are overloaded - including assigment.

> What happens with floating point types? Can values overflow to infinity
> or is this trapped? How about divide by zero or indeed zero/zero
> (NaN)? What about underflow?

currently only integer types are addressed. Damion Vicino has take on
task of extending the library to floating point types. He is a post
doctoral student at INRIA and I believe he is well suited to the task.
Turns out that implementing "safe" functionality for floating point
numbers has a completely different set of issues and considerations.
I'm sure this is not news to you. it's almost a separate library. He
worked on this as a Google Summer of Code project. If you want to lend
a hand to him this, I'm sure it would be appreciated - and, very, very,

BTW - Since I have a (fatal) tendency to think big, I named the library
Safe Numerics rather than Safe Integer. But I think the safe integer is
very useful in it's own right.

> And finally, I think there needs to be good constexpr support - in fact
> that could be the killer feature that sets the library apart.

The implementation contains a module which does compile time range
arithmetic which is all constexpr. Before exploiting this, I was stuck
- now I'm free. BTW - the library ( version)
requires gcc 6.0+ in order to compile - due to constexpr problems in
previous gcc compilers - I don't know about msvc.

> Finally your documents title is "Java Printing" which you may wish to
> correct ;)

What does it take to get a break here?

Robert Ramey

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