Re: Re[2]: boolean operators

[Nick Gammon <nick@...>]

On 30/09/2006, at 4:48 AM, David Jones wrote:

> Actually I think NG was suggesting an approach where the parser,  
> having eaten an 'x' say, changes the lexer state so that the next  
> '+' is tokenised as part of a number, not as the token '+'.

An interesting side-effect of the modified parser/lexer is that it is  
slightly faster. Why?

Consider the case of this statement: a = -2

In standard Lua the lexer processes 4 tokens: a, =, -, 2

In the modified version we only have 3 tokens: a, =, -2

Thus we save a trip through the lexer, and probably a bit of code in  
the parser as well.

My timings:

Original Lua:

$ echo 'for i = 1,1000000 do loadstring "a = -2" end' | time lua
18.63user 0.00system 0:18.63elapsed 99%CPU (0avgtext+0avgdata  
0maxresident)k
0inputs+0outputs (189major+30minor)pagefaults 0swaps

Modified Lua:

$ echo 'for i = 1,1000000 do loadstring "a = -2" end' | time lua.ng
18.06user 0.00system 0:18.07elapsed 99%CPU (0avgtext+0avgdata  
0maxresident)k
0inputs+0outputs (185major+30minor)pagefaults 0swaps


The modified version runs in 96% of the time taken by the original  
version.

- Nick