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Subject: Re: [boost] New Boost.XInt Library, request preliminary review
From: Scott McMurray ([hidden])
Date: 2010-03-29 20:42:21

On 29 March 2010 02:32, Chad Nelson <chad.thecomfychair_at_[hidden]> wrote:
> Not completely. There *are* the two functions that return Not-a-Number
> as part of their normal operation, not counting the string- and
> stream-reading functions. As I said on the rationales page of the
> documentation, I tried using Boost.Optional for those, but it made the
> library harder for people not already familiar with Boost.Optional to
> understand. An error code is an idiom that every C or C++ developer
> already understands well and knows how to deal with.

Those two functions, invmod and random_prime, can use xint() as their
error code, if the relevant exception is blocked, since 0 is obviously
neither a multiplicative inverse or a prime. That even lets you use
them like error codes:

    xint z = invmod(x, y);
    if (z) { ... worked ... }
    else { ... no inverse exists ... }

Though personally I think I'd still prefer an exception. If I'm doing
RSA and there's no inverse, something has gone drastically wrong.

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