1 files changed, 41 insertions, 0 deletions
diff --git a/bank.c b/bank.c
new file mode 100644
index 0000000..02b4522
--- /dev/null
+++ b/bank.c
@@ -0,0 +1,41 @@
+#include <stdint.h>
+#include "bignum.h"
+
+char would_overflow(unsigned long value, unsigned long amount) {
+	return ((UINT32_MAX - amount) <= value);
+}
+
+char bank_withdraw(long amount) {
+	bignum(bigamt);
+
+	if(amount < 0) {
+		/* can't withdraw all, if too much in bank */
+		if(big_cmp(&bank, B_MAXLONG) == 1)
+			return 0;
+		
+		big_copy(&bigamt, &bank);
+		big_to_ulong(&bigamt, &amount);
+	}
+
+	if(would_overflow(cash, amount)) return 0;
+
+	cash += amount;
+	ulong_to_big(&amount, &bigamt);
+	big_sub(&bank, &bank, &bigamt);
+
+	return 1;
+}
+
+void bank_deposit(long amount) {
+	bignum bigamt;
+
+	if(amount < 0) amount = cash;
+
+	cash -= amount;
+	ulong_to_big(&amount, &bigamt);
+	big_add(&bank, &bank, &bigamt);
+}
+
+void bank_interest(void) {
+	big_mul(&bank, &bank, &interest_rate);
+}