I forgot what exactly I changed

marcie.go

@@ -31,6 +31,7 @@ const (
 	JUMPI    Opcode = 0xC
 	LOADI    Opcode = 0xD
 	STOREI   Opcode = 0xE
+	MOD      Opcode = 0xF
 )
 
 // Instruction provides a convenient way to create an instruction word
@@ -158,6 +159,15 @@ func (machine *Machine) Execute (offset int16) (err error) {
 			// Store indirect: Use X the value at X as the address
 			// of where to store the value
 			machine.memory[memoryValue] = machine.accumulator
+			
+		case MOD:
+			// Set AC to the remainder of AC divided by the value at
+			// X
+			if memoryValue == 0 {
+				machine.accumulator = 0
+			} else {
+				machine.accumulator %= memoryValue
+			}
 
 		default:
 			err = ErrorUnknownInstruction

masm/main.go

@@ -38,6 +38,7 @@ var mnemonics = map[string] marcie.Opcode {
 	"jumpi":    marcie.JUMPI,
 	"loadi":    marcie.LOADI,
 	"storei":   marcie.STOREI,
+	"mod":      marcie.MOD,
 	"org":      ORG,
 }