Happy New Years

New friends.

Happy new year to all! I hope this year is exciting as the last!

I hope this year is exciting

I think it is in a Kai Lung story (Ernest Bramah) that the phrase may you live in interesting times is uttered as a curse.

And FPU support in RiscLua :)

And FPU support in RiscLua

The business of numbers in RiscLua has exercised my mind for quite a while, and I am very glad to have feedback and suggestions on the topic – especially now that Lua 5.3 is about to be finalized. As you may know, the standard Lua distribution has doubles for its default number system. That is fine for most 64-bit systems, but not so fine for the ARM CPUs to which RISC OS has until recently been tied, especially as their floating point operations are implemented in software, and so are slow. See http://www.wra1th.plus.com/lua/version.html for how RiscLua has tried to fudge things over the years.

Briefly, the stages were:
1. Use doubles — inefficient (2002)
2. Use 32-bit integers — no fp numbers (2002)
3. Use MAPM for arbitrary size numbers (2004)
4. Extend VM for bitwise operations (2006)
5. Add doubles as heap objects (2006)
6. Replace doubles with bc fixed point numbers (2012)
I do not think RISC OS platforms are (yet?) appropriate for serious number crunching. The bc-number system is OK for light use of numbers with decimal points – in fact does not financial software use fixed, not floating, point?

It would be nice to be able to use hard VFP2 rather than soft FP on the Raspberry Pi. When C libraries
become available that implement the usual mathlib functions using VFP2, then I think it would be worth bringing out a new version of RiscLua with doubles the default, like the standard Lua distribution. The main point behind Lua 5.3 is supposed to be untangling integer from floating point numbers in the sources.

There is much controversy about coercion between number types. Do you maintain strong typing or, in the belief that it makes life easier for the innumerate, pretend that numbers are numbers and try to protect the innocent public from the rigours of mathematics? My own preference is for strong typing. However, when Lua was born they had to go with the second strategy.