ESOJAY wrote:
It allows long long. I'm just not sure if long long is always going to be 64
bits on any machine I port the code to.
The situation is a little bit screwy ...
The C99 Standard requires `long long' to be at least 64
bits wide, but permits it to be wider. If you need 64 bits
or more but don't want to waste space if `long long' turns
out to be 128 bits, say, use `int_least64_t' from <stdint.h>.
Still in C99, if you need *exactly* 64 bits you can use
`int64_t', also from <stdint.h>. However, C99 does not require
that this type be supported by all implementations , so you can't
count on it being available. It may be enough that your code
will fail to compile on such an implementation; the person
attempting to port it will at least be ade aware of the trouble.
The earlier C90 Standard did not define `long long' --
in fact, using `long long' in a program was a syntax error.
Still, many compilers provided it as an extension when
invoked in a non-strict mode. About the best you can do
is to hope that such compilers also "advertise" the fact
through the <limits.h> macros, so you can test at compile
time whether a suitable `long long' exists. Making the
test is just a bit tricky because the preprocessor may
not be able to handle such large values; here's one way:
#include <limits.h>
#if (LLONG_MAX >> 31) >> 31 == 1
typedef long long int64;
#else
#error "No 64-bit integer type!"
#endif
(Obviously, you could change `==' to `>=' if you need an
"at least" rather than an "exactly" 64-bit type.)
This isn't 100% certain to work, though. `LLONG_MAX'
is mandated by C99 but was (obviously) absent from C90,
and a compiler that decided to provide `long long' before
C99 appeared might not have described the type in exactly
the same way C99 would eventually require. Also, the
support for `long long' in things like printf() may not
be exactly what C99 eventually specified. Still, a test
like this is probably the best you can do for a pre-C99
implementation.
--
Er*********@sun .com 
