Andrei Alexandrescu wrote:
dsimcha wrote:
== Quote from Andrei Alexandrescu (seewebsiteforem...@erdani.org)'s
article
Walter Bright wrote:
John Reimer wrote:
Hello Walter,
You know, the unimplemented 128 bit integer types.
Does anyone have a use for these?
Was that "cent" and "ucent"?
yes.
Would any of these map well to SSE Instructions on Intel CPU's?
Not a chance :-(
Then it looks like we better leave large fixed-size integers to a
library.
Andrei
Something that I still don't think has been made very clear in this
discussion
that I'm very curious about: How efficient would these large
fixed-size ints be
(on 32-bit hardware)? Would they be almost as fast as 64-bit, almost
as slow as
bigints, or somewhere roughly in the middle? Obviously on 64-bit
hardware they
can be made fast, but if that's the only place they can be made fast,
then I think
it's more important that DMD support 64-bit hardware first.
Assume we define a FixedInt(uint bits) structure. That would contain the
value in-situ so there is no dynamic allocation, no indirection, and
full-blown copying. For built-in sizes, FixedInt will alias itself away,
for example:
template FixedInt(uint n) if (n == 8) { alias byte FixedInt; }
template FixedInt(uint n) if (n == 16) { alias short FixedInt; }
template FixedInt(uint n) if (n == 32) { alias int FixedInt; }
template FixedInt(uint n) if (n == 64) { alias long FixedInt; }
That's nice because it allows you to use FixedInt with a parameterized
size throughout, yet still take advantage of builtin optimizations
whenever applicable.
For the larger sizes and operations my guess would be that FixedInt will
be close to what can be achieved via built-ins.
Andrei
is it possible to make int/long/short/etc internal to the compiler and
use the above FixedInt in the language? there shouldn't be any
performance differences between an old-style int and the above
FixedInt!(32), for instance.
this way all the different types are reduced to one built-in type that
looks like a template. similar to the way C++ uses the template syntax
for casts like static_cast<type>(var) even though it's usually
implemented inside the compiler.
also, this approch can be expanded to eliminate also size_t (which to me
seems ugly).
libs could perhaps extend the same interface and add a BigInt as well.
