Merge pull request #3 from s1na/eth_multicallv1

add rationale for pre-computed calls

docs/ethsimulatev1-notes.md

@@ -191,3 +191,14 @@ Clients may introduce their own limits to prevent DOS attacks using the method.
 - How many blocks can be defined in `BlockStateCalls`. The suggested default for this is 256 blocks
 - A global gas limit (similar to the same limit for `eth_call`). The eth_simulate cannot exceed the global gas limit over its lifespan
 - The clients can set their own limit on how big the input JSON payload can be. A suggested default for this is 30mb
+
+## Rationale
+
+### Pre-computed calls
+
+When it comes to contract override behavior, specifically precompile override, there were two approaches:
+
+1. As specified above to allow replacement of precompiles by EVM code and to allow those same precompiles to be relocated to another access for fallback behavior.
+2. Allow users to pass in a set of pre-computed calls for an address, i.e. direct mapping of input to output.
+
+The second approach has better UX for simple use-cases such as faking a signature via ecrecover. It also allows for getting the same gas usage as a real precompile execution. The simpler UX comes at cost of flexibility. Overriding with EVM code is general. It also imposes changes to the EVM interpreter code, which has been otherwise avoided, without enabling new features. Hence the spec proposes the first alternative.