Migrate instruction encoding to external library

The PowerPC instruction encoder and patching logic is now available at https://github.com/wii-tools/powerpc.

go.mod

@@ -6,5 +6,6 @@ require (
 	github.com/logrusorgru/aurora/v3 v3.0.0
 	github.com/wii-tools/GoNUSD v0.2.2
 	github.com/wii-tools/arclib v1.0.0
+	github.com/wii-tools/powerpc v0.0.0-20220411041712-104089eba964
 	github.com/wii-tools/wadlib v0.3.1
 )

go.sum

@@ -4,5 +4,7 @@ github.com/wii-tools/GoNUSD v0.2.2 h1:vHiSLI9sK9Q4zbCt24jMiq/lo2FISLBuCHoaY3Bd88
 github.com/wii-tools/GoNUSD v0.2.2/go.mod h1:Wf0ZMf4jdyQYSaSmNyFsqfQbngFA/cM9mpJBZ63Qlzs=
 github.com/wii-tools/arclib v1.0.0 h1:OAmbL3NDUmlR0wa1VpJhxnKiIRFZz1CC40lTVPUm8Ms=
 github.com/wii-tools/arclib v1.0.0/go.mod h1:uXFan/NSXoQ2pOVPN4ugZ4nJX7esBnjB1QUgVrEzK/4=
+github.com/wii-tools/powerpc v0.0.0-20220411041712-104089eba964 h1:/ZeMBIoblxzyhKHQJncvBZaxqi6RZz4rm4QvL0QiguA=
+github.com/wii-tools/powerpc v0.0.0-20220411041712-104089eba964/go.mod h1:bt/52tMfh1hmEXwFh1i1AOEMNHoe0jSXkcRunOSdFkc=
 github.com/wii-tools/wadlib v0.3.1 h1:g0Szzof/YsBLghP+JpoVzT/6M6jpl+AH9PHiUuG3cd8=
 github.com/wii-tools/wadlib v0.3.1/go.mod h1:GK+f2POk+rVu1p4xqLSb4ll1SKKbfOO6ZAB+oPLV3uQ=

main.go

@@ -6,6 +6,7 @@ import (
 	"github.com/logrusorgru/aurora/v3"
 	"github.com/wii-tools/GoNUSD"
 	"github.com/wii-tools/arclib"
+	"github.com/wii-tools/powerpc"
 	"github.com/wii-tools/wadlib"
 	"io/fs"
 	"io/ioutil"
@@ -137,6 +138,22 @@ func main() {
 	writeOut("patched.wad", output)
 }
 
+// applyDefaultPatches applies the default patches to our main DOL.
+func applyDefaultPatches() {
+	var err error
+
+	mainDol, err = powerpc.ApplyPatchSet(OverwriteIOSPatch, mainDol)
+	check(err)
+	mainDol, err = powerpc.ApplyPatchSet(LoadCustomCA(), mainDol)
+	check(err)
+	mainDol, err = powerpc.ApplyPatchSet(PatchBaseDomain(), mainDol)
+	check(err)
+	mainDol, err = powerpc.ApplyPatchSet(NegateECTitle, mainDol)
+	check(err)
+	mainDol, err = powerpc.ApplyPatchSet(PatchECCfgPath, mainDol)
+	check(err)
+}
+
 // check has an anxiety attack if things go awry.
 func check(err error) {
 	if err != nil {

modify_dol.go

@@ -1,98 +0,0 @@
-package main
-
-import (
-	"bytes"
-	"errors"
-	"fmt"
-
-	"github.com/logrusorgru/aurora/v3"
-)
-
-var (
-	ErrInconsistentPatch = errors.New("before and after data present within file are not the same size")
-	ErrPatchOutOfRange   = errors.New("patch cannot be applied past binary size")
-	ErrInvalidPatch      = errors.New("before data present within patch did not exist in file")
-)
-
-// Patch represents a patch applied to the main binary.
-type Patch struct {
-	// Name is an optional name for this patch.
-	// If present, its name will be logged upon application.
-	Name string
-
-	// AtOffset is the offset within the file this patch should be applied at.
-	// If not present, the patch will be recursively applied across the entire file.
-	// Relying on this behavior is highly discouraged, as it may damage other parts of the binary
-	// if gone unchecked.
-	AtOffset int
-
-	// Before is an array of the bytes to find for, i.e. present within the original file.
-	Before []byte
-
-	// After is an array of the bytes to replace with.
-	After []byte
-}
-
-// PatchSet represents multiple patches available to be applied.
-type PatchSet []Patch
-
-// applyPatch applies the given patch to the main DOL.
-func applyPatch(patch Patch) error {
-	// Print name if present
-	if patch.Name != "" {
-		fmt.Println(" + Applying patch", aurora.Cyan(patch.Name))
-	}
-
-	// Ensure consistency
-	if len(patch.Before) != len(patch.After) {
-		return ErrInconsistentPatch
-	}
-	if patch.AtOffset != 0 && patch.AtOffset > len(mainDol) {
-		return ErrPatchOutOfRange
-	}
-
-	// Either Before or After should return the same length.
-	patchLen := len(patch.Before)
-
-	// Determine our patching behavior.
-	if patch.AtOffset != 0 {
-		// Ensure original bytes are present
-		originalBytes := mainDol[patch.AtOffset : patch.AtOffset+patchLen]
-		if !bytes.Equal(originalBytes, patch.Before) {
-			return ErrInvalidPatch
-		}
-
-		// Apply patch at the specified offset
-		copy(mainDol[patch.AtOffset:], patch.After)
-	} else {
-		// Recursively apply this patch.
-		// We cannot verify if the original contents are present via this.
-		mainDol = bytes.ReplaceAll(mainDol, patch.Before, patch.After)
-	}
-
-	return nil
-}
-
-// applyPatchSet iterates through all possible patches, noting their name.
-func applyPatchSet(setName string, set PatchSet) {
-	fmt.Printf("Handling patch set \"%s\":\n", aurora.Yellow(setName))
-
-	for _, patch := range set {
-		err := applyPatch(patch)
-		check(err)
-	}
-}
-
-// emptyBytes returns an empty byte array of the given length.
-func emptyBytes(length int) []byte {
-	return bytes.Repeat([]byte{0x00}, length)
-}
-
-// applyDefaultPatches iterates through a list of default patches.
-func applyDefaultPatches() {
-	applyPatchSet("Overwrite IOS Syscall for ES", OverwriteIOSPatch)
-	applyPatchSet("Load Custom CA within IOS", LoadCustomCA())
-	applyPatchSet("Change Base Domain", PatchBaseDomain())
-	applyPatchSet("Negate EC Title Check", NegateECTitle)
-	applyPatchSet("Change EC Configuration Path", PatchECCfgPath)
-}

patch_base_domain.go

@@ -1,6 +1,10 @@
 package main
 
-import "strings"
+import (
+	"strings"
+
+	. "github.com/wii-tools/powerpc"
+)
 
 const (
 	NintendoBaseDomain = "shop.wii.com"
@@ -15,39 +19,42 @@ const (
 // See docs/patch_base_domain.md for more information.
 func PatchBaseDomain() PatchSet {
 	return PatchSet{
-		Patch{
+		Name: "Change Base Domain",
+		Patches: []Patch{
+			{
 				Name: "Modify /startup domain",
 
 				Before: []byte(ShowManualURL),
 				After:  padReplace(ShowManualURL),
 			},
-		Patch{
+			{
 				Name:     "Modify oss-auth URL",
 				AtOffset: 3180692,
 
 				Before: []byte(GetLogURL),
 				After:  padReplace(GetLogURL),
 			},
-		Patch{
+			{
 				Name:     "Modify trusted base domain prefix",
 				AtOffset: 3323432,
 
 				Before: []byte(TrustedDomain),
 				After:  padReplace(TrustedDomain),
 			},
-		Patch{
+			{
 				Name:     "Modify ECS SOAP endpoint URL",
 				AtOffset: 3268896,
 
 				Before: []byte(ECommerceBaseURL),
 				After:  padReplace(ECommerceBaseURL),
 			},
-		Patch{
+			{
 				Name: "Wildcard replace other instances",
 
 				Before: []byte(NintendoBaseDomain),
 				After:  padReplace(baseDomain),
 			},
+		},
 	}
 }
 
@@ -60,5 +67,5 @@ func padReplace(url string) []byte {
 	}
 
 	padding := len(url) - len(replaced)
-	return append([]byte(replaced), emptyBytes(padding)...)
+	return append([]byte(replaced), EmptyBytes(padding)...)
 }

patch_custom_ca.go

@@ -1,19 +1,25 @@
 package main
 
+import (
+	. "github.com/wii-tools/powerpc"
+)
+
 // LoadCustomCA loads our custom certificate, either generated or loaded,
 // into the IOS trust store for EC usage.
 // It is assumed that rootCertificate has been loaded upon invoking this patchset.
 // See docs/patch_custom_ca_ios.md for more information.
 func LoadCustomCA() PatchSet {
 	return PatchSet{
-		Patch{
+		Name: "Load Custom CA within IOS",
+		Patches: []Patch{
+			{
 				Name:     "Insert custom CA into free space",
 				AtOffset: 3037368,
 
-			Before: emptyBytes(len(rootCertificate)),
+				Before: EmptyBytes(len(rootCertificate)),
 				After:  rootCertificate,
 			},
-		Patch{
+			{
 				Name:     "Modify NHTTPi_SocSSLConnect to load cert",
 				AtOffset: 644624,
 
@@ -67,7 +73,7 @@ func LoadCustomCA() PatchSet {
 					LI(R3, 0xfc14),
 					// b FUNCTION_PROLOG
 					B(0x800acb10, 0x800acbb0),
-			}.toBytes(),
+				}.Bytes(),
 				After: Instructions{
 					// Our certificate is present at 0x802e97b8.
 					// r4 is the second parameter of SSLSetRootCA, the ca_cert pointer.
@@ -98,7 +104,8 @@ func LoadCustomCA() PatchSet {
 
 					// NOP the rest in order to allow execution to continue.
 					NOP(), NOP(), NOP(), NOP(), NOP(), NOP(), NOP(),
-			}.toBytes(),
+				}.Bytes(),
+			},
 		},
 	}
 }

patch_ec_cfg_path.go

@@ -1,11 +1,17 @@
 package main
 
+import (
+	. "github.com/wii-tools/powerpc"
+)
+
 var PatchECCfgPath = PatchSet{
-	Patch{
 	Name: "Change EC Configuration Path",
+	Patches: []Patch{
+		{
 			AtOffset: 3319968,
 
 			Before: []byte("ec.cfg\x00\x00"),
 			After:  []byte("osc.cfg\x00"),
 		},
+	},
 }

patch_ec_title_check.go

@@ -1,6 +1,13 @@
 package main
 
+import (
+	. "github.com/wii-tools/powerpc"
+)
+
 var NegateECTitle = PatchSet{
+	Name: "Negate EC Title Check",
+
+	Patches: []Patch{
 		Patch{
 			Name:     "Permit downloading all titles",
 			AtOffset: 619648,
@@ -9,13 +16,13 @@ var NegateECTitle = PatchSet{
 			Before: Instructions{
 				STWU(R1, R1, 0xffe0),
 				MFSPR(),
-		}.toBytes(),
+			}.Bytes(),
 
 			// Immediately return true
 			After: Instructions{
 				LI(R3, 1),
 				BLR(),
-		}.toBytes(),
+			}.Bytes(),
 		},
 		Patch{
 			Name:     "Mark all titles as managed",
@@ -24,11 +31,11 @@ var NegateECTitle = PatchSet{
 			Before: Instructions{
 				STWU(R1, R1, 0xfff0),
 				MFSPR(),
-		}.toBytes(),
+			}.Bytes(),
 			After: Instructions{
 				LI(R3, 1),
 				BLR(),
-		}.toBytes(),
+			}.Bytes(),
 		},
 		Patch{
 			Name:     "Mark all tickets as managed",
@@ -36,11 +43,11 @@ var NegateECTitle = PatchSet{
 			Before: Instructions{
 				STWU(R1, R1, 0xfff0),
 				MFSPR(),
-		}.toBytes(),
+			}.Bytes(),
 			After: Instructions{
 				LI(R3, 1),
 				BLR(),
-		}.toBytes(),
+			}.Bytes(),
 		},
 		Patch{
 			Name:     "Nullify ec::removeAllTitles",
@@ -48,10 +55,11 @@ var NegateECTitle = PatchSet{
 			Before: Instructions{
 				STWU(R1, R1, 0xffc0),
 				MFSPR(),
-		}.toBytes(),
+			}.Bytes(),
 			After: Instructions{
 				LI(R3, 0),
 				BLR(),
-		}.toBytes(),
+			}.Bytes(),
+		},
 	},
 }

patch_overwrite.go

@@ -1,9 +1,15 @@
 package main
 
+import (
+	. "github.com/wii-tools/powerpc"
+)
+
 // OverwriteIOSPatch effectively nullifies IOSC_VerifyPublicKeySign.
 // See docs/patch_overwrite_ios.md for more information.
 var OverwriteIOSPatch = PatchSet{
-	Patch{
+	Name: "Overwrite IOS Syscall for ES",
+	Patches: []Patch{
+		{
 			Name:     "Clear extraneous functions",
 			AtOffset: 20272,
 
@@ -29,30 +35,30 @@ var OverwriteIOSPatch = PatchSet{
 				// b printf
 				Instruction{0x48, 0x2a, 0x8b, 0x5c},
 
-			padding,
+				Padding,
 
 				// Function: textinput::EventObserver::onSE
 				BLR(),
-			padding, padding, padding,
+				Padding, Padding, Padding,
 				// Function: textinput::EventObserver::onEvent
 				BLR(),
-			padding, padding, padding,
+				Padding, Padding, Padding,
 				// Function: textinput::EventObserver::onCommand
 				BLR(),
-			padding, padding, padding,
+				Padding, Padding, Padding,
 				// Function: textinput::EventObserver::onInput
 				BLR(),
-			padding, padding, padding,
+				Padding, Padding, Padding,
-		}.toBytes(),
+			}.Bytes(),
 
 			// We wish to clear extraneous blrs so that our custom overwriteIOSMemory
 			// function does not somehow conflict.
 			// We only preserve onSE, which is this immediate BLR.
 			After: append(Instructions{
 				BLR(),
-		}.toBytes(), emptyBytes(108)...),
+			}.Bytes(), EmptyBytes(108)...),
 		},
-	Patch{
+		{
 			Name:     "Repair textinput::EventObserver vtable",
 			AtOffset: 3095452,
 
@@ -76,7 +82,7 @@ var OverwriteIOSPatch = PatchSet{
 				0x80, 0x01, 0x43, 0xf0,
 			},
 		},
-	Patch{
+		{
 			Name:     "Repair ipl::keyboard::EventObserver vtable",
 			AtOffset: 3097888,
 
@@ -99,11 +105,11 @@ var OverwriteIOSPatch = PatchSet{
 				0x80, 0x01, 0x43, 0xf0, // textinput::EventObserver::doNothing
 			},
 		},
-	Patch{
+		{
 			Name:     "Insert patch table",
 			AtOffset: 3205088,
 
-		Before: emptyBytes(52),
+			Before: EmptyBytes(52),
 			After: []byte{
 				//////////////
 				// PATCH #1 //
@@ -176,13 +182,13 @@ var OverwriteIOSPatch = PatchSet{
 				0x93, 0x00, 0x01, 0xff,
 			},
 		},
-	Patch{
+		{
 			Name:     "Insert overwriteIOSMemory",
 			AtOffset: 20276,
 
 			// This area should be cleared in the patch
 			// "Clear extraneous functions".
-		Before: emptyBytes(108),
+			Before: EmptyBytes(108),
 			After: Instructions{
 				// Our patch table is available at 0x803126e0.
 				LIS(R8, 0x8031),
@@ -248,28 +254,29 @@ var OverwriteIOSPatch = PatchSet{
 
 				// We're finished patching!
 				BLR(),
-		}.toBytes(),
+			}.Bytes(),
 		},
-	Patch{
+		{
 			Name:     "Do not require input for exception handler",
 			AtOffset: 32032,
 			Before: Instructions{
 				STWU(R1, R1, 0xFC10),
-		}.toBytes(),
+			}.Bytes(),
 			After: Instructions{
 				BLR(),
-		}.toBytes(),
+			}.Bytes(),
 		},
-	Patch{
+		{
 			Name:     "Modify ipl::Exception::__ct",
 			AtOffset: 31904,
 
 			Before: Instructions{
 				BLR(),
-		}.toBytes(),
+			}.Bytes(),
 			After: Instructions{
 				// b overwriteIOSMemory
 				Instruction{0x42, 0x80, 0xd2, 0x94},
-		}.toBytes(),
+			}.Bytes(),
+		},
 	},
 }

powerpc.go

@@ -1,152 +0,0 @@
-package main
-
-// uint24 returns
-func uint24(num uint32) [3]byte {
-	if num > 0x00FFFFFF {
-		panic("invalid uint24 passed")
-	}
-
-	result := fourByte(num)
-	return [3]byte{result[1], result[2], result[3]}
-}
-
-// Instruction represents a 4-byte PowerPC instruction.
-type Instruction [4]byte
-
-// Instructions represents a group of PowerPC instructions.
-type Instructions []Instruction
-
-// toBytes returns the bytes necessary to represent these instructions.
-func (i Instructions) toBytes() []byte {
-	var contents []byte
-
-	for _, instruction := range i {
-		contents = append(contents, instruction[:]...)
-	}
-
-	return contents
-}
-
-// padding is not an actual instruction - it represents 4 zeros.
-var padding Instruction = [4]byte{0x00, 0x00, 0x00, 0x00}
-
-// BLR represents the blr mnemonic on PowerPC.
-func BLR() Instruction {
-	return [4]byte{0x4E, 0x80, 0x00, 0x20}
-}
-
-// CRXOR represents a common use of CRXOR on PowerPC.
-// TODO: actually implement
-func CRXOR() Instruction {
-	return [4]byte{0x4c, 0xc6, 0x31, 0x82}
-}
-
-// ADDI represents the addi PowerPC instruction.
-func ADDI(rT Register, rA Register, value uint16) Instruction {
-	return EncodeInstrDForm(14, rT, rA, value)
-}
-
-// LI represents the li mnemonic on PowerPC.
-func LI(rT Register, value uint16) Instruction {
-	return ADDI(rT, 0, value)
-}
-
-// SUBI represents the subi mnemonic on PowerPC.
-// TODO: handle negative values properly?
-func SUBI(rT Register, rA Register, value uint16) Instruction {
-	return ADDI(rT, 0, -value)
-}
-
-// ADDIS represents the addis PowerPC instruction.
-func ADDIS(rT Register, rA Register, value uint16) Instruction {
-	return EncodeInstrDForm(15, rT, rA, value)
-}
-
-// LIS represents the lis mnemonic on PowerPC.
-func LIS(rT Register, value uint16) Instruction {
-	return ADDIS(rT, 0, value)
-}
-
-// ORI represents the ori PowerPC instruction.
-func ORI(rS Register, rA Register, value uint16) Instruction {
-	return EncodeInstrDForm(24, rS, rA, value)
-}
-
-// STH represents the sth PowerPC instruction.
-func STH(rS Register, offset uint16, rA Register) Instruction {
-	return EncodeInstrDForm(44, rS, rA, offset)
-}
-
-// EIEIO represents the eieio PowerPC instruction.
-func EIEIO() Instruction {
-	return [4]byte{0x7C, 0x00, 0x06, 0xAC}
-}
-
-// STW represents the stw PowerPC instruction.
-func STW(rS Register, offset uint16, rA Register) Instruction {
-	return EncodeInstrDForm(36, rS, rA, offset)
-}
-
-// LWZ represents the lwz PowerPC instruction.
-func LWZ(rT Register, offset uint16, rA Register) Instruction {
-	return EncodeInstrDForm(32, rT, rA, offset)
-}
-
-// NOP represents the nop mnemonic for PowerPC.
-func NOP() Instruction {
-	return ORI(R0, R0, 0)
-}
-
-// CMPWI represents the cmpwi mnemonic for PowerPC.
-// It does not support any other CR fields asides from 0.
-func CMPWI(rA Register, value uint16) Instruction {
-	return EncodeInstrDForm(11, 0, rA, value)
-}
-
-// SYNC is a hack, hardcoding sync 0.
-// TODO(spotlightishere): actually encode this
-func SYNC() Instruction {
-	return [4]byte{0x7c, 0x00, 0x04, 0xac}
-}
-
-// MTSPR is a hack, hardcoding LR, r0.
-// TODO(spotlightishere): actually encode this
-func MTSPR() Instruction {
-	return [4]byte{0x7c, 0x08, 0x03, 0xa6}
-}
-
-// MFSPR is a hack, hardcoding r0, LR.
-// TODO(spotlightishere): actually encode this
-func MFSPR() Instruction {
-	return [4]byte{0x7c, 0x08, 0x02, 0xa6}
-}
-
-// STWU represents the stwu PowerPC instruction.
-func STWU(rS Register, rA Register, offset uint16) Instruction {
-	return EncodeInstrDForm(37, rS, rA, offset)
-}
-
-// calcDestination determines the proper offset from a given
-// calling address and target address.
-func calcDestination(from uint, target uint) [3]byte {
-	// TODO(spotlightishere): Handle negative offsets properly
-	offset := target - from
-
-	// Sign-extend by two bytes
-	calc := uint32(offset >> 2)
-	return uint24(calc)
-}
-
-// BL represents the bl PowerPC instruction.
-// It calculates the offset from the given current address and the given
-// target address, saving the current address in the link register. It then branches.
-func BL(current uint, target uint) Instruction {
-	return EncodeInstrIForm(18, calcDestination(current, target), false, true)
-}
-
-// B represents the b PowerPC instruction.
-// It calculates the offset from the given current address
-// and the given target address, and then branches.
-func B(current uint, target uint) Instruction {
-	return EncodeInstrIForm(18, calcDestination(current, target), false, false)
-}

powerpc_encoding.go

@@ -1,160 +0,0 @@
-package main
-
-import (
-	"encoding/binary"
-)
-
-// Register represents a value for a PowerPC register.
-type Register byte
-
-const (
-	R0 = iota
-	R1
-	R2
-	R3
-	R4
-	R5
-	R6
-	R7
-	R8
-	R9
-	R10
-	R11
-	R12
-	R13
-	R14
-	R15
-	R16
-	R17
-	R18
-	R19
-	R20
-	R21
-	R22
-	R23
-	R24
-	R25
-	R26
-	R27
-	R28
-	R29
-	R30
-	R31
-)
-
-// Bits represents bits for a byte.
-// If set, considered as 1. If not, 0.
-type Bits [8]bool
-
-// getBits returns a usable array of bits for the given byte.
-func getBits(in byte) Bits {
-	return [8]bool{
-		(in>>7)&1 == 1,
-		(in>>6)&1 == 1,
-		(in>>5)&1 == 1,
-		(in>>4)&1 == 1,
-		(in>>3)&1 == 1,
-		(in>>2)&1 == 1,
-		(in>>1)&1 == 1,
-		in&1 == 1,
-	}
-}
-
-// getByte returns the byte represented by these bits.
-func (b Bits) getByte() byte {
-	var result byte
-	for idx, truthy := range b {
-		if truthy {
-			result |= 1 << (7 - idx)
-		}
-	}
-
-	return result
-}
-
-// EncodeInstrDForm handles encoding a given opcode, RT, RA and SI.
-// D-form assumes:
-//  - 6 bits for the opcode
-//  - 5 for rT
-//  - 5 for rA
-//  - 16 for SI
-func EncodeInstrDForm(opcode byte, rT Register, rA Register, value uint16) Instruction {
-	var instr [2]Bits
-	opBits := getBits(opcode)
-	rTBits := getBits(byte(rT))
-	rABits := getBits(byte(rA))
-
-	instr[0] = Bits{
-		// We need the upper six bits for our opcode.
-		opBits[2],
-		opBits[3],
-		opBits[4],
-		opBits[5],
-		opBits[6],
-		opBits[7],
-		// Next, the lower two bits for rT.
-		rTBits[3],
-		rTBits[4],
-	}
-	instr[1] = Bits{
-		// Third, the lower three bits for rT.
-		rTBits[5],
-		rTBits[6],
-		rTBits[7],
-		// Finally, all five lowest bits for rA.
-		rABits[3],
-		rABits[4],
-		rABits[5],
-		rABits[6],
-		rABits[7],
-	}
-
-	firstInstr := instr[0].getByte()
-	secondInstr := instr[1].getByte()
-	valByte := twoByte(value)
-
-	return Instruction{firstInstr, secondInstr, valByte[0], valByte[1]}
-}
-
-// EncodeInstrIForm handles encoding a given opcode, LI, AA and LK.
-// I-form assumes:
-//   - 6 bits for the opcode
-//   - 24 bits for LI
-//   - 1 bit for absolute (AA)
-//   - 1 bit for should store in link register (LK)
-func EncodeInstrIForm(opcode byte, LI [3]byte, AA bool, LK bool) Instruction {
-	opBits := getBits(opcode)
-	liOne := getBits(LI[0])
-	liTwo := getBits(LI[1])
-	liThree := getBits(LI[2])
-
-	instr := [4]Bits{
-		{
-			// We need the upper six bits for our opcode.
-			opBits[2], opBits[3], opBits[4], opBits[5], opBits[6], opBits[7],
-			// Otherwise, copy LI as-is.
-			liOne[0], liOne[1],
-		},
-		{
-			liOne[2], liOne[3], liOne[4], liOne[5], liOne[6], liOne[7], liTwo[0], liTwo[1],
-		},
-		{
-			liTwo[2], liTwo[3], liTwo[4], liTwo[5], liTwo[6], liTwo[7], liThree[0], liThree[1],
-		},
-		{
-			liThree[2], liThree[3], liThree[4], liThree[5], liThree[6], liThree[7],
-			// Copy AA and LK as-is.
-			AA,
-			LK,
-		},
-	}
-
-	return Instruction{instr[0].getByte(), instr[1].getByte(), instr[2].getByte(), instr[3].getByte()}
-}
-
-// twoByte converts a uint16 to two big-endian bytes.
-func twoByte(passed uint16) [2]byte {
-	result := make([]byte, 2)
-	binary.BigEndian.PutUint16(result, passed)
-	return [2]byte{result[0], result[1]}
-}