feat: replace manual BigInt conversion with parseFixed for dEuro Savings (#2344)

cw_core/lib/parse_fixed.dart

@@ -0,0 +1,38 @@
+BigInt parseFixed(String value, int? decimals) {
+  decimals ??= 0;
+  final multiplier = getMultiplier(decimals);
+
+// Is it negative?
+  final negative = (value.substring(0, 1) == "-");
+  if (negative) value = value.substring(1);
+
+  if (value == ".") throw Exception("missing value, value, $value");
+
+// Split it into a whole and fractional part
+  final comps = value.split(".");
+  if (comps.length > 2) {
+    throw Exception("too many decimal points, value, $value");
+  }
+
+  var whole = comps.isNotEmpty ? comps[0] : "0";
+  var fraction = (comps.length == 2 ? comps[1] : "0").padRight(decimals, "0");
+
+  // Check the fraction doesn't exceed our decimals size
+  if (fraction.length > multiplier.length - 1) {
+    throw Exception(
+        "fractional component exceeds decimals, underflow, parseFixed");
+  }
+
+  final wholeValue = BigInt.parse(whole);
+  final fractionValue = BigInt.parse(fraction);
+  final multiplierValue = BigInt.parse(multiplier);
+
+  var wei = (wholeValue * multiplierValue) + fractionValue;
+
+  if (negative) wei *= BigInt.from(-1);
+
+  return wei;
+}
+
+// Returns a string "1" followed by decimal "0"s
+String getMultiplier(int decimals) => "1".padRight(decimals + 1, "0");

lib/view_model/integrations/deuro_view_model.dart

@@ -1,11 +1,10 @@
-import 'dart:math';
-
 import 'package:cake_wallet/core/execution_state.dart';
 import 'package:cake_wallet/ethereum/ethereum.dart';
 import 'package:cake_wallet/store/app_store.dart';
 import 'package:cake_wallet/view_model/send/send_view_model_state.dart';
 import 'package:cw_core/pending_transaction.dart';
 import 'package:cw_core/wallet_type.dart';
+import 'package:cw_core/parse_fixed.dart';
 import 'package:mobx/mobx.dart';
 
 part 'deuro_view_model.g.dart';
@@ -82,7 +81,7 @@ abstract class DEuroViewModelBase with Store {
   Future<void> prepareSavingsEdit(String amountRaw, bool isAdding) async {
     try {
       state = TransactionCommitting();
-      final amount = BigInt.from(num.parse(amountRaw) * pow(10, 18));
+      final amount = parseFixed(amountRaw, 18);
       final priority = _appStore.settingsStore.priority[WalletType.ethereum]!;
       transaction = await (isAdding
           ? ethereum!.addDEuroSaving(_appStore.wallet!, amount, priority)