use amount_msat_mul_div operation to compute fees

Changelog-None

Signed-off-by: Lagrang3 <[email protected]>

Author: Lagrang3

common/amount.c

@@ -581,11 +581,9 @@ bool amount_msat_fee(struct amount_msat *fee,
 	 *    - fee_base_msat + ( amount_to_forward * fee_proportional_millionths / 1000000 )
 	 */
 	fee_base.millisatoshis = fee_base_msat;
-
-	if (mul_overflows_u64(amt.millisatoshis, fee_proportional_millionths))
+	if (!amount_msat_mul_div(&fee_prop, amt, fee_proportional_millionths,
+				 1000000))
 		return false;
-	fee_prop.millisatoshis = amt.millisatoshis * fee_proportional_millionths
-		/ 1000000;
 
 	return amount_msat_add(fee, fee_base, fee_prop);
 }

common/test/run-amount.c

@@ -85,6 +85,23 @@ static void test_amount_sub_fee(struct amount_msat msat,
 	assert(amount_msat_greater(in2, in));
 }
 
+static void test_amount_fee(struct amount_msat msat, u32 base, u32 prop,
+			    struct amount_msat expected_msat)
+{
+	struct amount_msat fee;
+	assert(amount_msat_fee(&fee, msat, base, prop));
+	assert(amount_msat_eq(fee, expected_msat));
+}
+
+static void test_amount_fee_str(const char *msat_str, u32 base, u32 prop,
+				u64 expected)
+{
+	struct amount_msat msat;
+	struct amount_msat expected_msat = amount_msat(expected);
+	assert(parse_amount_msat(&msat, msat_str, strlen(msat_str)));
+	return test_amount_fee(msat, base, prop, expected_msat);
+}
+
 static void test_amount_with_fee(void)
 {
 	for (int basebits = 0; basebits < 33; basebits++) {
@@ -93,13 +110,57 @@ static void test_amount_with_fee(void)
 		for (int propbits = 0; propbits < 20; propbits++) {
 			u32 prop = (1ULL << propbits);
 
-			for (int amtbits1 = 0; amtbits1 < 42; amtbits1++) {
-				for (int amtbits2 = 0; amtbits2 < 42; amtbits2++) {
+			for (int amtbits1 = 0; amtbits1 < 63; amtbits1++) {
+				for (int amtbits2 = 0; amtbits2 < 63; amtbits2++) {
 					test_amount_sub_fee(amount_msat((1ULL << amtbits1) | (1ULL << amtbits2)), base, prop);
 				}
 			}
 		}
 	}
+
+	for (int basebits = 0; basebits < 33; basebits++) {
+		u32 base = (1ULL << basebits);
+		for (int propbits = 0; propbits < 20; propbits++) {
+			u32 prop = (1ULL << propbits);
+			test_amount_fee(amount_msat(0), base, prop,
+					amount_msat(base));
+		}
+	}
+	for (int basebits = 0; basebits < 33; basebits++) {
+		u32 base = (1ULL << basebits);
+		for (int amtbits = 0; amtbits < 63; amtbits++)
+			test_amount_fee(amount_msat(1ULL << amtbits), base, 0,
+					amount_msat(base));
+	}
+	for (int amtbits = 0; amtbits < 63; amtbits++)
+		test_amount_fee(amount_msat(1ULL << amtbits), 0, 0,
+				amount_msat(0));
+
+	test_amount_fee_str("1msat", 1, 1, 1);
+	test_amount_fee_str("1msat", 1, 500000, 1);
+	test_amount_fee_str("1msat", 1, 1000000, 2);
+
+	test_amount_fee_str("1msat", 1234567890, 1, 1234567890ULL);
+	test_amount_fee_str("1msat", 1234567890, 500000, 1234567890ULL);
+	test_amount_fee_str("1msat", 1234567890, 1000000, 1234567891ULL);
+
+	test_amount_fee_str("1btc", 1, 1, 100001ULL);
+	test_amount_fee_str("1btc", 1, 500000, 50000000001ULL);
+	test_amount_fee_str("1btc", 1, 1000000, 100000000001ULL);
+
+	test_amount_fee_str("1btc", 1234567890, 1, 1234667890ULL);
+	test_amount_fee_str("1btc", 1234567890, 500000, 51234567890ULL);
+	test_amount_fee_str("1btc", 1234567890, 1000000, 101234567890ULL);
+
+	test_amount_fee_str("21000000btc", 1, 1, 2100000000001ULL);
+	test_amount_fee_str("21000000btc", 1, 500000, 1050000000000000001ULL);
+	test_amount_fee_str("21000000btc", 1, 1000000, 2100000000000000001ULL);
+
+	test_amount_fee_str("21000000btc", 1234567890, 1, 2101234567890ULL);
+	test_amount_fee_str("21000000btc", 1234567890, 500000,
+			    1050000001234567890ULL);
+	test_amount_fee_str("21000000btc", 1234567890, 1000000,
+			    2100000001234567890ULL);
 }
 
 #define FAIL_MSAT(msatp, str)					\