Minor day 7 optimisations

Each VM doesn't need its own opcode array (hopefully); use a
pre-allocated memory bank for the memory of all amplifiers.

07/main.go

 	"github.com/csmith/aoc-2019/intcode"
 )
 
-func copyOf(memory []int) []int {
-	res := make([]int, len(memory))
-	copy(res, memory)
-	return res
-}
-
-func runPipeline(program []int, ps []int, feedback bool) int {
+func runPipeline(memoryBanks []int, program []int, ps []int, feedback bool) int {
 	// Create a series of VMs for our amplifiers
 	vms := make([]*intcode.VirtualMachine, len(ps))
 	for i := 0; i < len(ps); i++ {
-		vms[i] = intcode.NewVirtualMachine(copyOf(program), true)
+		memory := memoryBanks[i*len(program) : (i+1)*len(program)]
+		copy(memory, program)
+		vms[i] = intcode.NewVirtualMachine(memory, true)
 	}
 
 	// Link all the inputs and outputs
 	return <-vms[len(vms)-1].Output
 }
 
-func maxOutput(input []int, ps []int, feedback bool) int {
+func maxOutput(memoryBanks []int, input []int, ps []int, feedback bool) int {
 	max := 0
 	for _, p := range common.Permutations(ps) {
-		val := runPipeline(input, p, feedback)
+		val := runPipeline(memoryBanks, input, p, feedback)
 		if val > max {
 			max = val
 		}
 
 func main() {
 	input := common.ReadCsvAsInts("07/input.txt")
-	fmt.Println(maxOutput(input, []int{0, 1, 2, 3, 4}, false))
-	fmt.Println(maxOutput(input, []int{5, 6, 7, 8, 9}, true))
+	memoryBanks := make([]int, len(input)*5)
+	fmt.Println(maxOutput(memoryBanks, input, []int{0, 1, 2, 3, 4}, false))
+	fmt.Println(maxOutput(memoryBanks, input, []int{5, 6, 7, 8, 9}, true))
 }

intcode/ops.go

 package intcode
 
-// OpcodeFunc is a function that describes an opcode implemented in the VM.
-type OpcodeFunc = func(vm *VirtualMachine)
+// opcodeFunc is a function that describes an opcode implemented in the VM.
+type opcodeFunc = func(vm *VirtualMachine)
 
-// AddOpcode takes the values specified by args 1 and 2, adds them together, and stores at the memory address given
+var opcodes = [100]opcodeFunc{
+	1:  addOpcode,
+	2:  mulOpcode,
+	3:  readOpCode,
+	4:  writeOpCode,
+	5:  jumpIfTrueOpCode,
+	6:  jumpIfFalseOpCode,
+	7:  lessThanOpCode,
+	8:  equalsOpCode,
+	99: haltOpcode,
+}
+
+// addOpcode takes the values specified by args 1 and 2, adds them together, and stores at the memory address given
 // by arg 3.
-func AddOpcode(vm *VirtualMachine) {
+func addOpcode(vm *VirtualMachine) {
 	vm.Memory[vm.Memory[vm.ip+3]] = vm.arg(0) + vm.arg(1)
 	vm.ip += 4
 }
 
-// MulOpcode takes the values specified by args 1 and 2, multiplies them together, and stores at the memory address
+// mulOpcode takes the values specified by args 1 and 2, multiplies them together, and stores at the memory address
 // given by arg 3.
-func MulOpcode(vm *VirtualMachine) {
+func mulOpcode(vm *VirtualMachine) {
 	vm.Memory[vm.Memory[vm.ip+3]] = vm.arg(0) * vm.arg(1)
 	vm.ip += 4
 }
 
-// ReadOpCode reads a value from the input stream and stores it at the memory address given by arg 1.
-func ReadOpCode(vm *VirtualMachine) {
+// readOpCode reads a value from the input stream and stores it at the memory address given by arg 1.
+func readOpCode(vm *VirtualMachine) {
 	vm.Memory[vm.Memory[vm.ip+1]] = <-vm.Input
 	vm.ip += 2
 }
 
-// WriteOpCode writes the value specified by the first argument to the output stream.
-func WriteOpCode(vm *VirtualMachine) {
+// writeOpCode writes the value specified by the first argument to the output stream.
+func writeOpCode(vm *VirtualMachine) {
 	vm.Output <- vm.arg(0)
 	vm.ip += 2
 }
 
-// JumpIfTrueOpCode checks if the first argument is not zero, and if so jumps to the second argument.
-func JumpIfTrueOpCode(vm *VirtualMachine) {
+// jumpIfTrueOpCode checks if the first argument is not zero, and if so jumps to the second argument.
+func jumpIfTrueOpCode(vm *VirtualMachine) {
 	if vm.arg(0) != 0 {
 		vm.ip = vm.arg(1)
 	} else {
 	}
 }
 
-// JumpIfFalseOpCode checks if the first argument is zero, and if so jumps to the second argument.
-func JumpIfFalseOpCode(vm *VirtualMachine) {
+// jumpIfFalseOpCode checks if the first argument is zero, and if so jumps to the second argument.
+func jumpIfFalseOpCode(vm *VirtualMachine) {
 	if vm.arg(0) == 0 {
 		vm.ip = vm.arg(1)
 	} else {
 	}
 }
 
-// LessThanOpCode checks if the first argument is less than the second, and stores the result at the address given
+// lessThanOpCode checks if the first argument is less than the second, and stores the result at the address given
 // by the third argument.
-func LessThanOpCode(vm *VirtualMachine) {
+func lessThanOpCode(vm *VirtualMachine) {
 	if vm.arg(0) < vm.arg(1) {
 		vm.Memory[vm.Memory[vm.ip+3]] = 1
 	} else {
 	vm.ip += 4
 }
 
-// EqualsOpCode checks if the first argument is equal to the second, and stores the result at the address given
+// equalsOpCode checks if the first argument is equal to the second, and stores the result at the address given
 // by the third argument.
-func EqualsOpCode(vm *VirtualMachine) {
+func equalsOpCode(vm *VirtualMachine) {
 	if vm.arg(0) == vm.arg(1) {
 		vm.Memory[vm.Memory[vm.ip+3]] = 1
 	} else {
 	vm.ip += 4
 }
 
-// HaltOpcode halts the VM and takes no arguments.
-func HaltOpcode(vm *VirtualMachine) {
+// haltOpcode halts the VM and takes no arguments.
+func haltOpcode(vm *VirtualMachine) {
 	vm.Halted = true
 }

intcode/vm.go

 
 // VirtualMachine is an IntCode virtual machine.
 type VirtualMachine struct {
-	ip      int
-	modes   uint8
-	opcodes [100]interface{}
-	Memory  []int
-	Halted  bool
-	Input   chan int
-	Output  chan int
+	ip     int
+	modes  uint8
+	Memory []int
+	Halted bool
+	Input  chan int
+	Output chan int
 }
 
 // NewVirtualMachine creates a new IntCode virtual machine, initialised
 		ip:     0,
 		Memory: memory,
 		Halted: false,
-		opcodes: [100]interface{}{
-			1:  AddOpcode,
-			2:  MulOpcode,
-			3:  ReadOpCode,
-			4:  WriteOpCode,
-			5:  JumpIfTrueOpCode,
-			6:  JumpIfFalseOpCode,
-			7:  LessThanOpCode,
-			8:  EqualsOpCode,
-			99: HaltOpcode,
-		},
 	}
 
 	if hasIO {
 			mask = mask << 1
 		}
 
-		vm.opcodes[opcode].(OpcodeFunc)(vm)
+		opcodes[opcode](vm)
 	}
 	if vm.Output != nil {
 		close(vm.Output)