use uint64 for balance, like other examples

examples/wrc20.nim

@@ -1,16 +1,16 @@
 ## ewasm “WRC20” token contract coding challenge
 ## https://gist.github.com/axic/16158c5c88fbc7b1d09dfa8c658bc363
 
-import ../eth_contracts, stint
+import ../eth_contracts, endians
 
 proc do_balance() =
   if getCallDataSize() != 24:
     revert(nil, 0)
 
-  var address: array[20, byte]
+  var address{.noinit.}: array[20, byte]
   callDataCopy(address, 4)
 
-  var balance: array[32, byte]
+  var balance{.noinit.}: array[32, byte]
   storageLoad(address, addr balance)
   finish(addr balance, sizeof(balance).int32)
 
@@ -22,7 +22,7 @@ proc do_transfer() =
   getCaller(addr sender)
   var recipient: array[20, byte]
   callDataCopy(recipient, 4)
-  var value: uint64
+  var value: array[8, byte]
   callDataCopy(value, 24)
 
   var senderBalance: array[32, byte]
@@ -30,18 +30,22 @@ proc do_transfer() =
   var recipientBalance: array[32, byte]
   storageLoad(recipient, addr recipientBalance)
 
-  var sb = readUintBE[256](senderBalance)
-  var rb = readUintBE[256](recipientBalance)
-  let v = value.u256
+  var sb, rb, v: uint64
+
+  bigEndian64(addr v, addr value)
+  bigEndian64(addr sb, addr senderBalance[32 - 8])
 
   if sb < v:
     revert(nil, 0)
 
-  sb -= v
-  rb += v
+  bigEndian64(addr rb, addr recipientBalance[32 - 8])
+
+  sb -= v
+  rb += v # TODO there's an overflow possible here..
+
+  bigEndian64(addr senderBalance[32 - 8], addr sb)
+  bigEndian64(addr recipientBalance[32 - 8], addr rb)
 
-  senderBalance = sb.toByteArrayBE()
-  recipientBalance = rb.toByteArrayBE()
   storageStore(sender, addr senderBalance)
   storageStore(recipient, addr recipientBalance)