blockchain: Optimize old block ver upgrade checks. #2912
Merged
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Currently the code that rejects old block versions once the majority of the network has upgraded is performed using a loop that iterates backwards from latest enforced block version while checking for a majority upgrade at each version. This is inefficient for blocks early in the chain since it means multiple versions need to be checked when it isn't really necessary.
This optimizes the relevant code by taking into account that the relevant enforcement semantics reduce to the following:
The following timing information obtained from profiling shows the overall reduction achieved with the optimized code for mainnet: