bitfield-epoch

A solidity library to efficiently compress user activations into a single 256 bit storage slot

Why?

Solidity uses 8 bits as its smallest 'native' type, and working with these in arrays is expensive. This library relies on some assumptions about epochs:

• Active users in epoch t are active in epochs t + k => k = 1...., K (unless they deactivate)
• Deactivated users in epoch t remain deactivated until they reactivate
• The user of this library has an awareness of the current epoch 4. Time moves strictly forward.

A bitfield is a 256 bit integer, indicating a user is active (1) or inactive (0) for epoch i.

Assuming a 1 month epoch, this allows us to store just over 21 years of activation history in a single storage slot.

Initialize the array when activating the user for the first time, indicating what epoch they have started from.

Activate or deactivate the user at specific epochs.

• Activating will set all subsequent epochs to active (1)
• Deactivating will set all subsequent epochs to inactive (0)

Check if a particular epoch is active or not using the isActivated function.

Finally, you can iterate back from the current epoch to check when was the last time the user is activated. Note: do not start from the last possible epoch (255) as 'activated' users will have all epochs by default set to active (1). Instead, start from the current epoch.

Setup

gh repo clone jordaniza/bitfield-epoch

forge build

# run tests:
forge test

See the test files for examples of use. Alternatively, there is a python script that you can run to show how the binary operations look like for 32 bits of data.