diff --git a/src/data_formats/parsing/quest/opcodes.ts b/src/data_formats/parsing/quest/opcodes.ts
index 8ccd66be..b628343e 100644
--- a/src/data_formats/parsing/quest/opcodes.ts
+++ b/src/data_formats/parsing/quest/opcodes.ts
@@ -122,10 +122,34 @@ export class Opcode {
         false,
         []
     ));
-    static readonly unknown_0a = (OPCODES[0x0a] = new Opcode(0x0a, "unknown_0a", [], false, []));
-    static readonly unknown_0b = (OPCODES[0x0b] = new Opcode(0x0b, "unknown_0b", [], false, []));
-    static readonly unknown_0c = (OPCODES[0x0c] = new Opcode(0x0c, "unknown_0c", [], false, []));
-    static readonly unknown_0d = (OPCODES[0x0d] = new Opcode(0x0d, "unknown_0d", [], false, []));
+    static readonly letb = (OPCODES[0x0a] = new Opcode(
+        0x0a,
+        "letb",
+        [{ type: Type.Register }, { type: Type.U8 }],
+        false,
+        []
+    ));
+    static readonly letw = (OPCODES[0x0b] = new Opcode(
+        0x0b,
+        "letw",
+        [{ type: Type.Register }, { type: Type.U16 }],
+        false,
+        []
+    ));
+    static readonly leta = (OPCODES[0x0c] = new Opcode(
+        0x0c,
+        "leta",
+        [{ type: Type.Register }, { type: Type.Register }],
+        false,
+        []
+    ));
+    static readonly leto = (OPCODES[0x0d] = new Opcode(
+        0x0d,
+        "leto",
+        [{ type: Type.Register }, { type: Type.U16 /* ILabel or DLabel */ }],
+        false,
+        []
+    ));
     static readonly unknown_0e = (OPCODES[0x0e] = new Opcode(0x0e, "unknown_0e", [], false, []));
     static readonly unknown_0f = (OPCODES[0x0f] = new Opcode(0x0f, "unknown_0f", [], false, []));
     static readonly set = (OPCODES[0x10] = new Opcode(
@@ -1262,7 +1286,7 @@ export class Opcode {
     ));
     static readonly sync_register = (OPCODES[0xef] = new Opcode(0xef, "sync_register", [], false, [
         { type: Type.Register },
-        { type: Type.U32 },
+        { type: Type.U32 /* TODO: Can be U32 or Register. */ },
     ]));
     static readonly send_regwork = (OPCODES[0xf0] = new Opcode(
         0xf0,
diff --git a/src/scripting/data_flow_analysis.test.ts b/src/scripting/data_flow_analysis.test.ts
new file mode 100644
index 00000000..4f0d0d2e
--- /dev/null
+++ b/src/scripting/data_flow_analysis.test.ts
@@ -0,0 +1,160 @@
+import { InstructionSegment, SegmentType } from "../data_formats/parsing/quest/bin";
+import { assemble } from "./assembly";
+import { create_control_flow_graph, BranchType } from "./data_flow_analysis";
+
+test("single instruction", () => {
+    const im = to_instructions(`
+        0:
+            ret
+    `);
+    const cfg = create_control_flow_graph(im);
+
+    expect(cfg.nodes.length).toBe(1);
+
+    expect(cfg.nodes[0].start).toBe(0);
+    expect(cfg.nodes[0].end).toBe(1);
+    expect(cfg.nodes[0].branch_type).toBe(BranchType.Return);
+    expect(cfg.nodes[0].from.length).toBe(0);
+    expect(cfg.nodes[0].to.length).toBe(0);
+    expect(cfg.nodes[0].branch_labels.length).toBe(0);
+});
+
+test("single unconditional jump", () => {
+    const im = to_instructions(`
+        0:
+            jmp 1
+        1:
+            ret
+    `);
+    const cfg = create_control_flow_graph(im);
+
+    expect(cfg.nodes.length).toBe(2);
+
+    expect(cfg.nodes[0].start).toBe(0);
+    expect(cfg.nodes[0].end).toBe(1);
+    expect(cfg.nodes[0].branch_type).toBe(BranchType.Jump);
+    expect(cfg.nodes[0].from.length).toBe(0);
+    expect(cfg.nodes[0].to.length).toBe(1);
+    expect(cfg.nodes[0].branch_labels.length).toBe(1);
+
+    expect(cfg.nodes[1].start).toBe(0);
+    expect(cfg.nodes[1].end).toBe(1);
+    expect(cfg.nodes[1].branch_type).toBe(BranchType.Return);
+    expect(cfg.nodes[1].from.length).toBe(1);
+    expect(cfg.nodes[1].to.length).toBe(0);
+    expect(cfg.nodes[1].branch_labels.length).toBe(0);
+});
+
+test("single conditional jump", () => {
+    const im = to_instructions(`
+        0:
+            jmp_= r1, r2, 1
+            ret
+        1:
+            ret
+    `);
+    const cfg = create_control_flow_graph(im);
+
+    expect(cfg.nodes.length).toBe(3);
+
+    expect(cfg.nodes[0].start).toBe(0);
+    expect(cfg.nodes[0].end).toBe(1);
+    expect(cfg.nodes[0].branch_type).toBe(BranchType.ConditionalJump);
+    expect(cfg.nodes[0].from.length).toBe(0);
+    expect(cfg.nodes[0].to.length).toBe(2);
+    expect(cfg.nodes[0].branch_labels.length).toBe(1);
+
+    expect(cfg.nodes[1].start).toBe(1);
+    expect(cfg.nodes[1].end).toBe(2);
+    expect(cfg.nodes[1].branch_type).toBe(BranchType.Return);
+    expect(cfg.nodes[1].from.length).toBe(1);
+    expect(cfg.nodes[1].to.length).toBe(0);
+    expect(cfg.nodes[1].branch_labels.length).toBe(0);
+
+    expect(cfg.nodes[2].start).toBe(0);
+    expect(cfg.nodes[2].end).toBe(1);
+    expect(cfg.nodes[2].branch_type).toBe(BranchType.Return);
+    expect(cfg.nodes[2].from.length).toBe(1);
+    expect(cfg.nodes[2].to.length).toBe(0);
+    expect(cfg.nodes[2].branch_labels.length).toBe(0);
+});
+
+test("single call", () => {
+    const im = to_instructions(`
+        0:
+            call 1
+            ret
+        1:
+            ret
+    `);
+    const cfg = create_control_flow_graph(im);
+
+    expect(cfg.nodes.length).toBe(3);
+
+    expect(cfg.nodes[0].start).toBe(0);
+    expect(cfg.nodes[0].end).toBe(1);
+    expect(cfg.nodes[0].branch_type).toBe(BranchType.Call);
+    expect(cfg.nodes[0].from.length).toBe(0);
+    expect(cfg.nodes[0].to.length).toBe(1);
+    expect(cfg.nodes[0].branch_labels.length).toBe(1);
+
+    expect(cfg.nodes[1].start).toBe(1);
+    expect(cfg.nodes[1].end).toBe(2);
+    expect(cfg.nodes[1].branch_type).toBe(BranchType.Return);
+    expect(cfg.nodes[1].from.length).toBe(1);
+    expect(cfg.nodes[1].to.length).toBe(0);
+    expect(cfg.nodes[1].branch_labels.length).toBe(0);
+
+    expect(cfg.nodes[2].start).toBe(0);
+    expect(cfg.nodes[2].end).toBe(1);
+    expect(cfg.nodes[2].branch_type).toBe(BranchType.Return);
+    expect(cfg.nodes[2].from.length).toBe(1);
+    expect(cfg.nodes[2].to.length).toBe(1);
+    expect(cfg.nodes[2].branch_labels.length).toBe(0);
+});
+
+test("conditional branch with fall-through", () => {
+    const im = to_instructions(`
+        0:
+            jmp_> r1, r2, 1
+            nop
+        1:
+            nop
+            ret
+    `);
+    const cfg = create_control_flow_graph(im);
+
+    expect(cfg.nodes.length).toBe(3);
+
+    expect(cfg.nodes[0].start).toBe(0);
+    expect(cfg.nodes[0].end).toBe(1);
+    expect(cfg.nodes[0].branch_type).toBe(BranchType.ConditionalJump);
+    expect(cfg.nodes[0].from.length).toBe(0);
+    expect(cfg.nodes[0].to.length).toBe(2);
+    expect(cfg.nodes[0].branch_labels.length).toBe(1);
+
+    expect(cfg.nodes[1].start).toBe(1);
+    expect(cfg.nodes[1].end).toBe(2);
+    expect(cfg.nodes[1].branch_type).toBe(BranchType.None);
+    expect(cfg.nodes[1].from.length).toBe(1);
+    expect(cfg.nodes[1].to.length).toBe(1);
+    expect(cfg.nodes[1].branch_labels.length).toBe(0);
+
+    expect(cfg.nodes[2].start).toBe(0);
+    expect(cfg.nodes[2].end).toBe(2);
+    expect(cfg.nodes[2].branch_type).toBe(BranchType.Return);
+    expect(cfg.nodes[2].from.length).toBe(2);
+    expect(cfg.nodes[2].to.length).toBe(0);
+    expect(cfg.nodes[2].branch_labels.length).toBe(0);
+});
+
+function to_instructions(assembly: string): InstructionSegment[] {
+    const { object_code, warnings, errors } = assemble(assembly.split("\n"));
+
+    expect(warnings).toEqual([]);
+    expect(errors).toEqual([]);
+
+    return object_code.filter(
+        segment => segment.type === SegmentType.Instructions
+    ) as InstructionSegment[];
+}
diff --git a/src/scripting/data_flow_analysis.ts b/src/scripting/data_flow_analysis.ts
new file mode 100644
index 00000000..e1eeed49
--- /dev/null
+++ b/src/scripting/data_flow_analysis.ts
@@ -0,0 +1,477 @@
+import {
+    Instruction,
+    InstructionSegment,
+    Opcode,
+    Segment,
+    SegmentType,
+} from "../data_formats/parsing/quest/bin";
+
+export enum BranchType {
+    None,
+    Return,
+    Jump,
+    ConditionalJump,
+    Call,
+}
+
+export class BasicBlock {
+    readonly from: BasicBlock[] = [];
+    readonly to: BasicBlock[] = [];
+
+    constructor(
+        readonly segment: InstructionSegment,
+        readonly start: number,
+        readonly end: number,
+        readonly branch_type: BranchType,
+        /**
+         * Either jumps or calls, depending on `branch_type`.
+         */
+        readonly branch_labels: number[]
+    ) {}
+
+    link_to(other: BasicBlock): void {
+        this.to.push(other);
+        other.from.push(this);
+    }
+}
+
+export class ControlFlowGraph {
+    readonly nodes: BasicBlock[] = [];
+}
+
+export function create_control_flow_graph(segments: InstructionSegment[]): ControlFlowGraph {
+    const cfg = new ControlFlowGraph();
+    /**
+     * Mapping of labels to basic blocks.
+     */
+    const label_blocks = new Map<number, BasicBlock>();
+
+    for (const segment of segments) {
+        const blocks = create_basic_blocks(segment);
+
+        if (blocks.length) {
+            cfg.nodes.push(...blocks);
+
+            for (const label of segment.labels) {
+                label_blocks.set(label, blocks[0]);
+            }
+        }
+    }
+
+    link_blocks(cfg, label_blocks);
+    return cfg;
+}
+
+function create_basic_blocks(segment: InstructionSegment): BasicBlock[] {
+    const blocks: BasicBlock[] = [];
+    const len = segment.instructions.length;
+    let start = 0;
+
+    for (let i = start; i < len; i++) {
+        const inst = segment.instructions[i];
+
+        let branch_type: BranchType;
+        let branch_labels: number[];
+
+        switch (inst.opcode) {
+            // Return.
+            case Opcode.ret:
+                branch_type = BranchType.Return;
+                branch_labels = [];
+                break;
+
+            // Unconditional jump.
+            case Opcode.jmp:
+                branch_type = BranchType.Jump;
+                branch_labels = [inst.args[0].value];
+                break;
+
+            // Conditional jumps.
+            case Opcode.jmp_on:
+            case Opcode.jmp_off:
+                branch_type = BranchType.ConditionalJump;
+                branch_labels = [inst.args[0].value];
+                break;
+            case Opcode.jmp_e:
+            case Opcode.jmpi_e:
+            case Opcode.jmp_ne:
+            case Opcode.jmpi_ne:
+            case Opcode.ujmp_g:
+            case Opcode.ujmpi_g:
+            case Opcode.jmp_g:
+            case Opcode.jmpi_g:
+            case Opcode.ujmp_l:
+            case Opcode.ujmpi_l:
+            case Opcode.jmp_l:
+            case Opcode.jmpi_l:
+            case Opcode.ujmp_ge:
+            case Opcode.ujmpi_ge:
+            case Opcode.jmp_ge:
+            case Opcode.jmpi_ge:
+            case Opcode.ujmp_le:
+            case Opcode.ujmpi_le:
+            case Opcode.jmp_le:
+            case Opcode.jmpi_le:
+                branch_type = BranchType.ConditionalJump;
+                branch_labels = [inst.args[2].value];
+                break;
+            case Opcode.switch_jmp:
+                branch_type = BranchType.ConditionalJump;
+                branch_labels = inst.args.slice(1).map(a => a.value);
+                break;
+
+            // Calls.
+            case Opcode.call:
+                branch_type = BranchType.Call;
+                branch_labels = [inst.args[0].value];
+                break;
+            case Opcode.va_call:
+                branch_type = BranchType.Call;
+                branch_labels = [inst.args[0].value];
+                break;
+            case Opcode.switch_call:
+                branch_type = BranchType.Call;
+                branch_labels = inst.args.slice(1).map(a => a.value);
+                break;
+
+            // All other opcodes.
+            default:
+                if (i === len - 1) {
+                    branch_type = BranchType.None;
+                    branch_labels = [];
+                    break;
+                } else {
+                    continue;
+                }
+        }
+
+        blocks.push(new BasicBlock(segment, start, i + 1, branch_type, branch_labels));
+        start = i + 1;
+    }
+
+    return blocks;
+}
+
+function link_blocks(cfg: ControlFlowGraph, label_blocks: Map<number, BasicBlock>): void {
+    // Pairs of calling block and block to which callees should return to.
+    const callers: [BasicBlock, BasicBlock][] = [];
+
+    for (let i = 0; i < cfg.nodes.length; i++) {
+        const block = cfg.nodes[i];
+        const next_block = cfg.nodes[i + 1];
+
+        switch (block.branch_type) {
+            case BranchType.Return:
+                continue;
+            case BranchType.Call:
+                if (next_block) {
+                    callers.push([block, next_block]);
+                }
+                break;
+            case BranchType.None:
+            case BranchType.ConditionalJump:
+                if (next_block) {
+                    block.link_to(next_block);
+                }
+                break;
+        }
+
+        for (const label of block.branch_labels) {
+            const to_block = label_blocks.get(label);
+
+            if (to_block) {
+                block.link_to(to_block);
+            }
+        }
+    }
+
+    for (const [caller, ret] of callers) {
+        link_returning_blocks(label_blocks, ret, caller);
+    }
+}
+
+/**
+ * Links returning blocks to their callers.
+ */
+function link_returning_blocks(
+    label_blocks: Map<number, BasicBlock>,
+    ret: BasicBlock,
+    block: BasicBlock
+): void {
+    for (const label of block.branch_labels) {
+        const sub_block = label_blocks.get(label);
+
+        if (sub_block) {
+            if (sub_block.branch_type === BranchType.Return) {
+                sub_block.link_to(ret);
+            }
+
+            link_returning_blocks(label_blocks, ret, sub_block);
+        }
+    }
+}
+
+/////////////////
+//    Crap:    //
+/////////////////
+
+class DfState {
+    private registers: DataView;
+
+    constructor(other?: DfState) {
+        if (other) {
+            this.registers = new DataView(other.registers.buffer.slice(0));
+        } else {
+            this.registers = new DataView(new ArrayBuffer(2 * 4 * 256));
+        }
+    }
+
+    get_min(register: number): number {
+        return this.registers.getInt32(2 * register);
+    }
+
+    get_max(register: number): number {
+        return this.registers.getInt32(2 * register + 1);
+    }
+
+    set(register: number, min: number, max: number): void {
+        this.registers.setInt32(2 * register, min);
+        this.registers.setInt32(2 * register + 1, max);
+    }
+
+    // getf(register: number): number {
+    //     return this.registers.getFloat32(2 * register);
+    // }
+
+    // setf(register: number, value: number): void {
+    //     this.registers.setFloat32(2 * register, value);
+    //     this.registers.setFloat32(2 * register + 1, value);
+    // }
+}
+
+/**
+ * @param segments mapping of labels to segments.
+ */
+function data_flow(
+    label_holder: any,
+    segments: Map<number, Segment>,
+    entry_label: number,
+    entry_state: DfState
+): void {
+    const segment = segments.get(entry_label);
+    if (!segment || segment.type !== SegmentType.Instructions) return;
+
+    let out_states: DfState[] = [new DfState(entry_state)];
+
+    for (const instruction of segment.instructions) {
+        const args = instruction.args;
+
+        for (const state of out_states) {
+            switch (instruction.opcode) {
+                case Opcode.let:
+                case Opcode.flet:
+                    state.set(
+                        args[0].value,
+                        state.get_min(args[1].value),
+                        state.get_max(args[1].value)
+                    );
+                    break;
+                case Opcode.leti:
+                case Opcode.letb:
+                case Opcode.letw:
+                case Opcode.leta:
+                case Opcode.sync_leti:
+                case Opcode.sync_register:
+                    state.set(args[0].value, args[1].value, args[1].value);
+                    break;
+                case Opcode.leto:
+                    {
+                        const info = label_holder.get_info(args[1].value);
+                        state.set(args[0].value, info ? info.offset : 0, info ? info.offset : 0);
+                    }
+                    break;
+                case Opcode.set:
+                    state.set(args[0].value, 1, 1);
+                    break;
+                case Opcode.clear:
+                    state.set(args[0].value, 0, 0);
+                    break;
+                case Opcode.leti:
+                case Opcode.letb:
+                case Opcode.letw:
+                case Opcode.leta:
+                case Opcode.sync_leti:
+                case Opcode.sync_register:
+                    state.set(args[0].value, args[1].value, args[1].value);
+                    break;
+                // case Opcode.fleti:
+                //     state.setf(args[0].value, args[1].value);
+                //     break;
+                case Opcode.rev:
+                    {
+                        const reg = args[0].value;
+                        const max = state.get_min(reg) <= 0 && state.get_max(reg) >= 0 ? 1 : 0;
+                        const min = state.get_min(reg) === 0 && state.get_max(reg) === 0 ? 1 : 0;
+                        state.set(reg, min, max);
+                    }
+                    break;
+                // case Opcode.add:
+                //     {
+                //         const reg = args[0].value;
+                //         state.set(reg, state.get_min(reg) + state.get_min(args[1].value));
+                //     }
+                //     break;
+                // case Opcode.addi:
+                //     {
+                //         const reg = args[0].value;
+                //         state.set(reg, state.get_min(reg) + args[1].value);
+                //     }
+                //     break;
+                // case Opcode.sub:
+                //     {
+                //         const reg = args[0].value;
+                //         state.set(reg, state.get_min(reg) - state.get_min(args[1].value));
+                //     }
+                //     break;
+                // case Opcode.subi:
+                //     {
+                //         const reg = args[0].value;
+                //         state.set(reg, state.get_min(reg) - args[1].value);
+                //     }
+                //     break;
+                // case Opcode.mul:
+                //     {
+                //         const reg = args[0].value;
+                //         state.set(reg, state.get_min(reg) * state.get_min(args[1].value));
+                //     }
+                //     break;
+                // case Opcode.muli:
+                //     {
+                //         const reg = args[0].value;
+                //         state.set(reg, state.get_min(reg) * args[1].value);
+                //     }
+                //     break;
+                // case Opcode.div:
+                //     {
+                //         const reg = args[0].value;
+                //         state.set(reg, state.get_min(reg) / state.get_min(args[1].value));
+                //     }
+                //     break;
+                // case Opcode.divi:
+                //     {
+                //         const reg = args[0].value;
+                //         state.set(reg, state.get_min(reg) / args[1].value);
+                //     }
+                //     break;
+                // case Opcode.and:
+                //     {
+                //         const reg = args[0].value;
+                //         state.set(reg, state.get_min(reg) & state.get_min(args[1].value));
+                //     }
+                //     break;
+                // case Opcode.andi:
+                //     {
+                //         const reg = args[0].value;
+                //         state.set(reg, state.get_min(reg) & args[1].value);
+                //     }
+                //     break;
+                // case Opcode.or:
+                //     {
+                //         const reg = args[0].value;
+                //         state.set(reg, state.get_min(reg) | state.get_min(args[1].value));
+                //     }
+                //     break;
+                // case Opcode.ori:
+                //     {
+                //         const reg = args[0].value;
+                //         state.set(reg, state.get_min(reg) | args[1].value);
+                //     }
+                //     break;
+                // case Opcode.xor:
+                //     {
+                //         const reg = args[0].value;
+                //         state.set(reg, state.get_min(reg) ^ state.get_min(args[1].value));
+                //     }
+                //     break;
+                // case Opcode.xori:
+                //     {
+                //         const reg = args[0].value;
+                //         state.set(reg, state.get_min(reg) ^ args[1].value);
+                //     }
+                //     break;
+                // case Opcode.mod:
+                //     {
+                //         const reg = args[0].value;
+                //         state.set(reg, state.get_min(reg) % state.get_min(args[1].value));
+                //     }
+                //     break;
+                // case Opcode.modi:
+                //     {
+                //         const reg = args[0].value;
+                //         state.set(reg, state.get_min(reg) % args[1].value);
+                //     }
+                //     break;
+                // case Opcode.shift_left:
+                //     {
+                //         const reg = args[0].value;
+                //         state.set(reg, state.get_min(reg) << state.get_min(args[1].value));
+                //     }
+                //     break;
+                // case Opcode.shift_right:
+                //     {
+                //         const reg = args[0].value;
+                //         state.set(reg, state.get_min(reg) >> state.get_min(args[1].value));
+                //     }
+                //     break;
+                // case Opcode.fadd:
+                //     {
+                //         const reg = args[0].value;
+                //         state.setf(reg, state.getf(reg) + state.getf(args[1].value));
+                //     }
+                //     break;
+                // case Opcode.faddi:
+                //     {
+                //         const reg = args[0].value;
+                //         state.setf(reg, state.getf(reg) + args[1].value);
+                //     }
+                //     break;
+                // case Opcode.fsub:
+                //     {
+                //         const reg = args[0].value;
+                //         state.setf(reg, state.getf(reg) - state.getf(args[1].value));
+                //     }
+                //     break;
+                // case Opcode.fsubi:
+                //     {
+                //         const reg = args[0].value;
+                //         state.setf(reg, state.getf(reg) - args[1].value);
+                //     }
+                //     break;
+                // case Opcode.fmul:
+                //     {
+                //         const reg = args[0].value;
+                //         state.setf(reg, state.getf(reg) * state.getf(args[1].value));
+                //     }
+                //     break;
+                // case Opcode.fmuli:
+                //     {
+                //         const reg = args[0].value;
+                //         state.setf(reg, state.getf(reg) * args[1].value);
+                //     }
+                //     break;
+                // case Opcode.fdiv:
+                //     {
+                //         const reg = args[0].value;
+                //         state.setf(reg, state.getf(reg) / state.getf(args[1].value));
+                //     }
+                //     break;
+                // case Opcode.fdivi:
+                //     {
+                //         const reg = args[0].value;
+                //         state.setf(reg, state.getf(reg) / args[1].value);
+                //     }
+                //     break;
+            }
+        }
+    }
+}