- What's the least number of words needed to write it?
- What's the most efficient implementation?
For example, take a look at Implementing
MIN in Forth without Conditional Code. The smallest version of MIN is 2 words shorter than eForth's MIN.Even words with a trivial implementation can pose an interesting problem. For example which of the following is most efficient:
Jones Forth TUCK
: TUCK DUP -ROT ;
Alternative TUCK
: TUCK SWAP OVER ;
If
DUP, -ROT, SWAP and OVER are all primitive, the alternative implementation will execute two fewer instructions on an 80x86 Forth. However, -ROT is often implemented in Forth which would cause the Jones Forth TUCK to be substantially slower. Here's a typical implementation of -ROT:: -ROT SWAP >R SWAP R> ;
If you can think of an alternative two word implementation of
TUCK or four word implementation of -ROT, please let me know. :-)
Premature optmisation is the root of all evil John! Finish it and then optimise!
ReplyDeleteCheers,
Ruben
Ruben: true, but only about 97% of the time ;-)
ReplyDelete"but only about 97% of the time ;-) "
ReplyDeleteGive examples of the 3%. If you don't finish it, then optimize, how do you know if a) you need to optimize, and b) if your "optimization" does any good.
In support of optimization: 1) it's fun, and 2) this is the core!
ReplyDelete--from someone who has implemented a Forth kernel before (on PowerPC).
Optimisation, in the '97% of the time, premature optimisation is the root of all evil' quote actually refers to 'micro-optimisation' which is about shaving a few processor cycles here and there.
ReplyDeleteAn example of the 3% would be when your optimisation forces larger changes...for example, in a software renderer, forcing power-of-two textures, allowing the use of bitshifts rather than multiplication and division.
: -ROT ROT ROT ;
ReplyDelete