Re:Baby's First Garbage Collector
by logancapaldo on Sunday December 08, 2013 @05:49PM
(#6871828)
What if it's not a DWIM compiler? I'm pretty sure (happy to be corrected) pointer <-> integer conversions are implementation defined. Therefore casting between could perform some reversible operation that ensured round tripping worked, but does not require that ptr(a - b) == a - b even though a == int(ptr(a)) holds.
[ Parent
| on HN ]
I'm pretty sure (happy to be corrected) pointer <-> integer conversions are implementation defined.
Quite correct, subject to the requirement that converting the same uintptr_t value back to (void ) will return the original pointer. So the conversion could be implemented as a hash table if the compiler author wanted.
But if you look carefully at what I wrote, I'm never converting a value which was not previously returned by a (void )->(uintptr_t) conversion.
Re:Baby's First Garbage Collector
by logancapaldo on Sunday December 08, 2013 @08:22PM
(#6872391)
I see. What I was worried about was a version of the code you didn't actually write (casting the ptrdiff_t result to a [u]intptr_t, not casting the pointers first).