Amounts

The Transaction API counts in satoshis (100,000,000 to one BSV), and uses BigInt for every amount. This way arithmetic never loses precision, including on the web, where int is a JavaScript number.

// Every amount in the Transaction API is a BigInt number of satoshis.
final amount = BigInt.from(150000); // 0.0015 BSV
final output = TransactionOutput(amount, SVScript());
output.satoshis; // BigInt 150000

Coin

Coin wraps a satoshi amount, along with conversions and arithmetic. The Interpreter takes the spent amount as a Coin (Coin.ofSat(satoshis)). To read a BSV amount that a user typed, we use Coin.ofBtc with a Decimal from package:decimal:

// Coin wraps a satoshi amount. Decimal comes from package:decimal.
final price = Coin.ofBtc(Decimal.parse('0.0015')); // from a user-entered BSV amount
price.getValue(); // BigInt 150000 satoshis

final balance = Coin.ofSat(BigInt.from(12345678));
balance.toBtc().toString(); // 0.12345678

final remaining = balance.subtract(price); // 12195678 satoshis
remaining.isGreaterThan(Coin.CENT); // true: Coin.CENT is 1000000 satoshis

The constants are Coin.ZERO, Coin.SATOSHI, Coin.MICROCOIN, Coin.MILLICOIN, Coin.CENT and Coin.COIN.

Coin.parseCoin is broken in 3.1.2

Coin.parseCoin and Coin.parseCoinInexact divide by 10⁸ instead of multiplying, so parseCoin('1') gives zero satoshis. Use Coin.ofBtc(Decimal.parse(text)) instead.