patch to fix constant math - 4th patch - the wide-int class - patch ping for the next stage 1

[Richard Biener]

On Wed, Feb 27, 2013 at 2:59 AM, Kenneth Zadeck
<zadeck@naturalbridge.com> wrote:
> This patch contains a large number of the changes requested by Richi.   It
> does not contain any of the changes that he requested to abstract the
> storage layer.   That suggestion appears to be quite unworkable.

I of course took this claim as a challenge ... with the following result.  It is
of course quite workable ;)

The attached patch implements the core wide-int class and three storage
models (fixed size for things like plain HWI and double-int, variable size
similar to how your wide-int works and an adaptor for the double-int as
contained in trees).  With that you can now do

HOST_WIDE_INT
wi_test (tree x)
{
  // template argument deduction doesn't do the magic we want it to do
  // to make this kind of implicit conversions work
  // overload resolution considers this kind of conversions so we
  // need some magic that combines both ... but seeding the overload
  // set with some instantiations doesn't seem to be possible :/
  // wide_int<> w = x + 1;
  wide_int<> w;
  w += x;
  w += 1;
  // template argument deduction doesn't deduce the return value type,
  // not considering the template default argument either ...
  // w = wi (x) + 1;
  // we could support this by providing rvalue-to-lvalue promotion
  // via a traits class?
  // otoh it would lead to sub-optimal code anyway so we should
  // make the result available as reference parameter and only support
  // wide_int <> res; add (res, x, 1); ?
  w = wi (x).operator+<wide_int<> >(1);
  wide_int<>::add(w, x, 1);
  return w.to_hwi ();
}

we are somewhat limited with C++ unless we want to get really fancy.
Eventually providing operator+ just doesn't make much sense for
generic wide-int combinations (though then the issue is its operands
are no longer commutative which I think is the case with your wide-int
or double-int as well - they don't suport "1 + wide_int" for obvious reasons).

So there are implementation design choices left undecided.

Oh, and the operation implementations are crap (they compute nonsense).

But you should get the idea.

Richard.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: my-wide-int.c
Type: text/x-csrc
Size: 9147 bytes
Desc: not available
URL: <http://gcc.gnu.org/pipermail/gcc-patches/attachments/20130402/6bf5f71b/attachment.bin>