Re: convert binary to decimal in template at compiler time.

From:

"Jim Langston" <tazmaster@rocketmail.com>

Newsgroups:

comp.lang.c++

Date:

Wed, 12 Sep 2007 02:42:34 -0700

Message-ID:

<swOFi.119$ss5.47@newsfe04.lga>

"Leo jay" <Python.LeoJay@gmail.com> wrote in message
news:1189587231.959150.319990@w3g2000hsg.googlegroups.com...

i'd like to implement a class template to convert binary numbers to
decimal at compile time.
and my test cases are:

BOOST_STATIC_ASSERT((bin<1111,1111,1111,1111>::value == 65535));
BOOST_STATIC_ASSERT((bin<1111>::value == 15));
BOOST_STATIC_ASSERT((bin<0>::value == 0));
BOOST_STATIC_ASSERT((bin<1010, 0011>::value == 163));

you can find my implementation at:
http://pastebin.org/2271

the first three cases were ok, but the last one failed, because,
compiler will parse 0011
as a octal number 9, instead of decimal number 11 because of the
leading 0s.

to resolve this, i defined 4 macros:

#define BIN1(a) bin<9##a>::value
#define BIN2(a, b) bin<9##a, 9##b>::value
#define BIN3(a, b, c) bin<9##a, 9##b, 9##c>::value
#define BIN4(a, b, c, d) bin<9##a, 9##b, 9##c, 9##d>::value

these macros could pass the last test case, but it's not good enough
that i have to specify how many numbers i will input.

is there any elegant way to resolve this?

thanks in advance.

Iteratore over the binary string backwards, raising by power of 2 and adding
up.
Untested code, presuming MyString contains binary string such as "10010010"
or whatever.
int value = 0;
int Multiplier = 1;
for ( int i = MyString.size() - 1; i >= 0; --i )
{
   if ( MyString[i] == '1' )
      value += Multiplier;
   Multiplier *= 2;
}

At the end value should have the binary value.

Now, since you have a decimal number you are trying to represent a binary
number with (not a good idea, you should go with strings or bit map) you
need to get it to a string. Easy method, use stringstream.