2009/5/27 Michael Meissner <meissner@xxxxxxxxxxxxxxxxxx>:
> On Tue, May 26, 2009 at 09:42:40PM -0700, me22 wrote:
>>
>> In my experience compilers are often even smart enough to have this
>> avoid the memory roundtrip, and it's undeniably legal:
>>
>> int ftoi(float x) {
>> int i;
>> memcpy(&i, &x, 4);
>> return i;
>> }
>
> Well from a pedantic point of view, it is only legal if sizeof (i) == sizeof
> (x) == 4, but you presumably already know that.
>
Agreed; I assumed we were operating under the ever-popular "there's
nothing but windows and linux on x86 or x64" delusion. Of course, the
union and other tricks are also architecture-dependant.
If I really wanted to do it properly, I'd use something like this:
template <typename F>
typename boost::uint_t<sizeof(F)*CHAR_BIT>::least
bitcast_to_integral(F f) {
typename boost::uint_t<sizeof(F)*CHAR_BIT>::least i = 0;
void *p = &i;
#ifdef BOOST_BIG_ENDIAN
p = (char*)p + (sizeof(i)-sizeof(f));
#endif
std::memcpy(&i, &f, sizeof(F));
return i;
}
But really, anything hacking around in float bit patterns is unlikely
to be portable enough to warrant such treatment.
