Is "repeat until not" better, worse or the same as "repeat while"

dbpage

Consider the following statement:

repeat until not lockset(namelock)

Does the above statement require more, less or the same execution time and memory than the following statement?

repeat while lockset(namelock)

Phil Pilgrim (PhiPi)

Code space and execution time are two things you can check on your own. For code space, just hit F8 in the PropTool to see how much is required for each version. For execution time, use two readings of cnt, subtracting the earlier one from the latter one to get the duration.

-Phil

kuroneko

re: execution time, it's a bit tricky with polling loops as it depends on when the lock state changes to trigger the exit path, e.g. changing shortly after the check adds another loop run before you can exit. In your case I'd stick with the while but write it like this (less space):

repeat
  while lockset(namelock)

Ariba

BST can generate a listing of the resulting bytecodes.
Here is the output a bit simplified:

repeat until not lockset(namelock)

Addr : 0018:       36     : Constant 2 $00000001
Addr : 0019:       2A     : LockSet(Id) Push
Addr : 001A:       FF     : Math Op NOT   
Addr : 001B:       0B 02  : jnz 001F  +2
Addr : 001D:       04 79  : Jmp 0018  -7   


                   repeat while lockset(namelock)

Addr : 001F:       36     : Constant 2 $00000001
Addr : 0020:       2A     : LockSet(Id) Push
Addr : 0021:       0A 02  : jz 0025   +2
Addr : 0023:       04 7A  : Jmp 001F  -6   

I would say that the WHILE version is faster because UNTIL NOT needs one bycode more. The other bytecodes are similar.

Andy