Transaction Value should be 256 bits

[jwasinger]

According to YP figure 16, tx value is 256 bits in size.

Hera is expecting a transaction value to be 128 bits: https://github.com/ewasm/hera/blob/master/src/eei.cpp#L607

I'm working on a fix but I'm stuck on trying to compare two evmc_uint256be to change this line: https://github.com/ewasm/hera/blob/master/src/eei.cpp#L880 . @axic @jakelang know of any code that does this?

[jwasinger]

YP omits a limit for the transaction value. The limit is 128 bits.