Improved documentation

src/arm/Mul.go

@@ -7,7 +7,7 @@ func MulRegisterRegister(destination cpu.Register, multiplicand cpu.Register, mu
 	return 0b10011011000<<21 | reg4(destination, multiplicand, multiplier, ZR)
 }
 
-// MultiplySubtract multiplies `multiplicand` with `multiplier`, subtracts `minuend` and saves the result in `destination`.
+// MultiplySubtract multiplies `multiplicand` with `multiplier`, subtracts the product from `minuend` and saves the result in `destination`.
 func MultiplySubtract(destination cpu.Register, multiplicand cpu.Register, multiplier cpu.Register, minuend cpu.Register) uint32 {
 	return 0b10011011000<<21 | 1<<15 | reg4(destination, multiplicand, multiplier, minuend)
 }

src/arm/Mul_test.go

@@ -34,6 +34,7 @@ func TestMultiplySubtract(t *testing.T) {
 		Code        uint32
 	}{
 		{arm.X0, arm.X1, arm.X2, arm.X3, 0x9B028C20},
+		{arm.X3, arm.X0, arm.X2, arm.X1, 0x9B028403},
 	}
 
 	for _, pattern := range usagePatterns {