Re: Rationale for an old TRUNCATE patch

[Adam Nemet <anemet at caviumnetworks dot com>]

Ian Lance Taylor writes:
> I'm not entirely sure, but I don't think Jim said the opposite.  He said
> that the way truncate works is machine dependent.  I said that the
> output of truncate is machine independent.  Since truncate is only
> defined for fixed-point modes, I think both statements are true.

OK but in that way every operation is machine dependent not just truncate.
BTW, why is being fixed-point relevant here?

>From that little excerpt I just gathered that maybe my misunderstanding of
treating truncate as a blackbox was not completely without precedence.  But
anyway I think I understand now.  JTBS, can you agree with other statement in
my email?:

> And IIUC this don't-care nature of the other bits that allows backends to
> define the upper bits.  For example to have sign-bit copies there in registers
> to enforce the MIPS64 SI mode representation.  And treating the don't care
> bits outside SI mode in this way is true for any other SI-mode operations
> performed on registers not just truncate, right?  Hmm, nice.

Thanks for all the explanations.

Adam