Amount input

[MathisGD]

Gas diff (sorry I don't know how @Rubilmax does his ones):

[Rubilmax]

Gas diff (sorry I don't know how @Rubilmax does his ones)

I'll never tell you it's my secret sauce

[Jean-Grimal]

IMO the best solution

[julien-devatom]

This is not so dirty to use a variable for a second usage. We use a specific int value (maxUint256) as a boolean. This is precisely what Ethereum does with the empty to field in a tx:
if to == undefined, then I call CREATE opcode, else call the code at the specified address.

The point is that this method is reducing the number of possibilities, such as "I want to withdraw 40% of my position"

[MerlinEgalite]

The point is that this method is reducing the number of possibilities, such as "I want to withdraw 40% of my position"

If you care about some wei yes.

Also another option is taking the max between the balance of the user and the amount passed as argument

[MerlinEgalite]

Well I've tried to create an alternative solution using the min between the amount passed and the balance of the user, but I'm facing to many roundings to make it a creadible alternative

[MathisGD]

ciao