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From: "msalters" <Michiel.Salters@logicacmg.com>
Newsgroups: comp.std.c++
Subject: Re: My nitpicks on n1774
Date: 9 May 2005 17:40:12 GMT
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"Daniel Kr�gler ne Spangenberg wrote:

> >[lib.integer.members] #8-#12: There could also be a constructor
> >that takes a range of chars delimited by two bidirectional
> >iterators.  Perhaps even remove the conversion from std::string
> >altogether.  integer(char const*) should still be kept because it
> >is so convenient with string literals.

> Why should your proposed char iterators be bidirectional?

I asssume because it's slightly easier to parse a number in reverse;
the basic algorithm is (using reverse_iterators)
integer base = 1;
for( ri = rbegin; ri != rend ; ++ri )
{
  value = base * (*ri);
  base *= 10;
}
Of course, the forward equivalent is
for( i = begin; i != end ; ++i )
{
  value = value * 10 + *i;
}
but I'm not sure if the base*=10 can be optimized better than
value*=10. Both are basically 2 bitshift operations and an
addition, but 10^N has N trailing zeroes that can be ignored.

Regards,
Michiel Salters.


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