research: gas usage for collateralizable

[dsshap]

the only benefit I can think of using this bitmap instead of a simple address => address => bool mapping is that it is cheaper to add data to the same storage (so setting multiple collateralizable asset1 for an asset0 will be cheaper). For reading it's not obvious why this will be cheaper because now every time you calculate isCollateralizable you need to do the bit operations instead of just reading a boolean directly.

Not sure which one is cheaper, to use a 2 layer mapping (with one more Keccak256 is 30 gas) or this bitmap.

Originally posted by @antoncoding in #2 (comment)