Numeric precision (WAM)

[tiagoantao]

Hi,

If I remember well, WAM based implementations of Prolog have issues with numeric precision: given that the WAM requires a few bits for tagging, numbers are never easy to represent in ways that go well with other languages.

Question: What is the status of Scryer regarding this? The FFI seemed OK with "normal" representations - but it would be nice to have a definitive view on this...

Many thanks

[bakaq]

As far as I know Scryer has arbitrary precision integers:

?- X is 10^100.
   X = 10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000.

[tiagoantao]

Thanks! That means that for FFI, there is no need to do any conversion work?

[bakaq]

Well, Scryer could make an integer that is too big for other languages (support for integers bigger than 64 bits is quite rare or depends on external libraries), and there you could have problems maybe.

[mthom]

It does have arbitrary precision integers. Also 56-bit signed fixnums.

[tiagoantao]

So, a sint64 on the FFI would be converted to a arbitrary precision or would there be a requirement that it only uses 56 bits from the C side? What about auint64? Thanks

[aarroyoc]

Currently, one needs to be very careful that the number you're passing into a foreign call is a Fixnum (in the 56 bits range). Otherwise, it will just simply not work, as it's not possible to convert an arbitrary precision integer to a sint64 or uint64 type. sint64 and uint64 are just 64 bit integers (signed and unsigned).