Incorrect satoshi rounding

[pokazef]

Some code is based on the assumption that satoshiAmount = int64(bitcoinAmount * 1e8). This seems to be incorrect. For example, the go code:

a := 3e-8
fmt.Println(int64(a * 1e8))

prints 2, not 3.

This happens in btcwallet.go, where the value of some UTXOs is off by one satoshi which makes the wallet balance report wrong. Here, using the btcutil.NewAmount function instead (which does correct rounding) would solve the problem.

But the issue seems to be present in other places (e.g. blockchain.go) which do not depend on btcutil and thus might need to be explicitly rounded.

[zavan]

I see an error that may be a result of this:

{
	"payment_error": "unable to route payment to destination: TemporaryChannelFailure: insufficient capacity in available outgoing links: need 175120982 mSAT, max available is 174696018 mSAT",
	"payment_preimage": "",
	"payment_route": null
}

Looks like it's picking up a route based on a rounded down value.

[Roasbeef]

@zavan I don't think that's related at all, this issue is isolated to the way we convert BTC from the rpc calls into satoshis that we'll use for manipulation internally.

[zavan]

@Roasbeef oh ok. That’s another problem I was getting earlier, it happened multiple times then later evolved into the ones I told you about on Twitter and #940, I can’t reproduce it anymore.