remove more int64 usage (#2369)

* remove more int64 usage

* explain loop bounds

beacon_chain/attestation_pool.nim

@@ -351,13 +351,19 @@ proc getAttestationsForBlock*(pool: var AttestationPool,
                               cache: var StateCache): seq[Attestation] =
   ## Retrieve attestations that may be added to a new block at the slot of the
   ## given state
-  let newBlockSlot = state.slot
+  let newBlockSlot = state.slot.uint64
   var attestations: seq[AttestationEntry]
 
   pool.updateAttestationsCache(state)
 
-  for i in max(1, newBlockSlot.int64 - ATTESTATION_LOOKBACK.int64) ..
-      newBlockSlot.int64:
+  # Consider attestations from the current slot and ranging back up to
+  # ATTESTATION_LOOKBACK slots, excluding the special genesis slot. As
+  # unsigned subtraction (mostly avoided in this codebase, partly as a
+  # consequence) will otherwise wrap through zero, clamp value which's
+  # subtracted so that slots through ATTESTATION_LOOKBACK don't do so.
+  for i in max(
+        1'u64, newBlockSlot - min(newBlockSlot, ATTESTATION_LOOKBACK)) ..
+      newBlockSlot:
     let maybeSlotData = getAttestationsForSlot(pool, i.Slot)
     if maybeSlotData.isSome:
       insert(attestations, maybeSlotData.get.attestations)

beacon_chain/validators/validator_duties.nim

@@ -583,8 +583,7 @@ proc updateValidatorMetrics*(node: BeaconNode) =
 
       if i < 64:
         attached_validator_balance.set(
-          min(balance, int64.high.uint64).int64,
-          labelValues = [shortLog(v.pubkey)])
+          balance.toGaugeValue, labelValues = [shortLog(v.pubkey)])
       else:
         inc i
       total += balance