On 07.12.2011 05:11, bcs wrote:
On 12/05/2011 11:20 PM, Don wrote:
On 06.12.2011 05:21, bcs wrote:
On 12/05/2011 08:37 AM, Don wrote:
On 05.12.2011 14:31, bearophile wrote:
Found through Reddit, two blog posts about how integers should behave
in system languages (with hardware support):
http://blog.regehr.org/archives/641
http://blog.regehr.org/archives/642
Bye,
bearophile
Not very convincing, since he proposes a change to existing
architectures, and seems completely unaware of the overflow flag.
I think he's looking at it form the language theory standpoint. As such,
architectures has nothing to do with it (the architectures to be
targeted has yet to be defined at that point)and getting access to the
overflow flag would require exposing it natively in the language.
It's not that he hasn't specified an architecture. It's a proposal which
does not work on _any_ existing architectures!
It's pure fantasy.
Well you can do it on x86. The fact the it doesn't provied hardware
traps is irrelevant. You might need to add a lot of branches but you can
get the semantics he is asking for.
That said, there is another interesting (but independent) question of
can it be done efficiently? You might have a very good question there,
but that isn't the question regehr is considering.
And he talks about NaN, when he means infinity. Floating point overflow
never results in a NaN.
You have a point there.
He doesn't seem to know anything about
saturating integer arithmetic, which exists in hardware (even x86
machines have supported a couple of operations since 1996).
Useless.
Again, he's not interested in the hardware implementation, he's only
interested in the defined semantics of the language, the things you can
count on regardless of that instruction set you are using. The fact the
x86 has saturating integer operations is moot because C doesn't have a
type the end up using them.
He's talking about system languages. A system language has to have a
close relationship to the architecture.
By contrast, if you don't care about performance, it's easy -- just use
BigInts for everything. Problem solved.
Looks like I have to put it more bluntly: I don't think he knows what
he's talking about. (On this particular topic).
