From: Gennaro Prota (gennaro_prota_at_[hidden])
Date: 2006-08-03 10:59:25
On Thu, 3 Aug 2006 11:35:19 +0100, "John Maddock"
<john_at_[hidden]> wrote:
>And the endianness of the float's if you're doing bit testing.
Which shouldn't be a problem for you ;-) Or just position/bitmask of
the sign bit.
>But of course if there is a macro already it's easy enough to convert it into a
>function.
Yep. Even if no macro exists you can perhaps hide the
machine-dependent stuff in one single "low-level primitive" function
upon which you can build all (or much of) the rest. I'm thinking to
something like
// your namespace...
enum type { finite, zero, nan, inf };
template <typename T>
type get_type(T t);
Also you could probably automatically generate much of the system
dependent stuff, for the most common systems. For instance:
// widely (not completely) portable
void calculate()
{
typedef float T; // for instance
typedef unsigned char byte;
T plus_1 ( 1 );
T minus_1( -1 );
const volatile byte * b_plus
= reinterpret_cast<const volatile byte *>(&plus_1);
const volatile byte * b_minus
= reinterpret_cast<const volatile byte *>(&minus_1);
int i = 0;
int bit = 0;
bool found = false;
for (i = 0; i < sizeof( T ); ++i )
{
for (bit = 0; bit < CHAR_BIT; ++bit)
{
const int mask = 1 << bit;
if( (b_plus[i] & mask)
!= (b_minus[i] & mask) )
{
assert(found == false);
found = true;
}
}
}
assert(found == true);
std::cout << "sign bit at byte " << (i-1)
<<", bit " << (bit-1) << '\n'
;
}
Ok, that will never compile but should give the idea. If any of the
asserts triggers just pretend nothing happened, calmly shut the
computer down and do not walk... run!
-- [ Gennaro Prota, C++ developer for hire ]