Change Bandwidth Price to Average for 24h Sliding Window

[arturalbov]

Change Bandwidth Price to Average for 24h Sliding Window

[hleb-albau]

1. I think we should better not to use double float conversion. It is not pure in terms of specification.
   May be we should have 2 methods: GetTxCost() -> int64 and GetPricedTxCost for such cases.
2. May be use BlockSpentBw as pointer everywhere, instead of making it fields pointers?

[arturalbov]

1. I think we should better not to use double float conversion. It is not pure in terms of specification.
   May be we should have 2 methods: **GetTxCost() -> int64** and **GetPricedTxCost** for such cases.

2. May be use  **BlockSpentBw** as pointer everywhere, instead of making it fields pointers?

@hleb-albau updated