From: George A. Heintzelman (georgeh_at_[hidden])
Date: 2001-07-02 11:29:30
> --- In boost_at_y..., <boost_at_y...> wrote:
> .) What about the low-level boolean operations,
> such as &,|,^:
> On the one hand, they are not really needed
> since std::bitset and std::vector<bool>
> already provide the respective functionality.
> Additionally, requiring these operators to be present
> might restrict every implementation to have a radix
> which is a power of 2; in particular,
> a BCD implementation would be excluded.
I doubt it would prevent them, but it WOULD make implementing these
operators rather inefficient in a non-base-2 radix.
Myself, I don't see the use for treating a big_int in a logical bitwise
way, given bitset (I don't like vector<bool>), so that would argue
against &, | and ^.
There are two problems I can think of, though. If it IS a base-2 radix,
one can almost certainly implement bitwise shifting operations used to
multiply by powers of 2, MUCH more efficiently than normal bignum
arithmetic. Given that the non-power-of-2 implementations can just
implement them as ordinary multiply/divides by 2, I think these ought
to be supplied.
Second, I can definitely see that people will want to hash big_ints,
and bitwise XOR is frequently used in such functions. Some tools
useable for getting good hashes out of bignums are necessary, if the
bitwise ops are not supplied.
> .) What should be syntax and semantics of a "div" function
> that returns quotient and remainder at the same time?
> I implemented a member function div(d,q)
> which returns *this /= d and sets q to the remainder.
> There are, however, many other possibilities.
This seems obvious:
returns pair<bignum,bignum> being the quotient and remainder.
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