From a31a1bc322af0c0852e040d60fa0680d62633587 Mon Sep 17 00:00:00 2001
From: David Souther <davidsouther+github@gmail.com>
Date: Thu, 11 Jan 2024 22:32:32 -0500
Subject: [PATCH 1/2] Start VM Builtins

---
 simulator/src/vm/builtins.test.ts | 21 ++++++++++++++++++++
 simulator/src/vm/builtins.ts      | 16 +++++++++++++++
 simulator/src/vm/vm.ts            | 33 +++++++++++++++++++------------
 3 files changed, 57 insertions(+), 13 deletions(-)
 create mode 100644 simulator/src/vm/builtins.test.ts
 create mode 100644 simulator/src/vm/builtins.ts

diff --git a/simulator/src/vm/builtins.test.ts b/simulator/src/vm/builtins.test.ts
new file mode 100644
index 000000000..0f46da450
--- /dev/null
+++ b/simulator/src/vm/builtins.test.ts
@@ -0,0 +1,21 @@
+import { unwrap } from "@davidsouther/jiffies/lib/esm/result.js";
+import { Vm } from "./vm.js";
+
+describe("builtins", () => {
+  describe("Math", () => {
+    test("multiply", () => {
+      const vm = unwrap(
+        Vm.build([
+          { op: "push", segment: "constant", offset: 7 },
+          { op: "push", segment: "constant", offset: 8 },
+          { op: "call", name: "Math.multiply", nArgs: 2 },
+        ])
+      );
+
+      vm.step();
+      vm.step();
+      vm.step();
+      expect(vm.read([0, 256])).toEqual([257, 56]);
+    });
+  });
+});
diff --git a/simulator/src/vm/builtins.ts b/simulator/src/vm/builtins.ts
new file mode 100644
index 000000000..67d867e3a
--- /dev/null
+++ b/simulator/src/vm/builtins.ts
@@ -0,0 +1,16 @@
+import { SCREEN_SIZE } from "../cpu/memory.js";
+import { VmMemory } from "./memory.js";
+
+export type VmBuiltin = (memory: VmMemory) => number;
+
+const BLANK_SCREEN = new Array(SCREEN_SIZE).fill(0);
+export const VM_BUILTINS: Record<string, VmBuiltin> = {
+  "Math.multiply": (memory) => {
+    const sp = memory.SP;
+    return (memory.get(sp - 2) * memory.get(sp - 1)) & 0xffff;
+  },
+  "Screen.clearScreen": (memory) => {
+    memory.screen.loadBytes(BLANK_SCREEN);
+    return 0;
+  },
+};
diff --git a/simulator/src/vm/vm.ts b/simulator/src/vm/vm.ts
index 6d1c3b3ab..ec7f2b4e5 100644
--- a/simulator/src/vm/vm.ts
+++ b/simulator/src/vm/vm.ts
@@ -8,6 +8,8 @@ import {
 import { FunctionInstruction, VmInstruction } from "../languages/vm.js";
 import { VmMemory } from "./memory.js";
 import { MemoryAdapter, RAM } from "../cpu/memory.js";
+import { VM_BUILTINS } from "./builtins.js";
+import { op } from "../util/asm.js";
 
 export type VmOperation =
   | FunctionOperation
@@ -492,19 +494,24 @@ export class Vm {
       }
       case "call": {
         const fnName = operation.name;
-        const fn = this.functionMap[fnName];
-        if (!fn) throw new Error(`Calling unknown function ${fnName}`);
-        const base = this.memory.pushFrame(
-          this.invocation.opPtr,
-          operation.nArgs,
-          fn.nVars
-        );
-        this.executionStack.push({
-          function: fnName,
-          opPtr: 0,
-          nArgs: operation.nArgs,
-          frameBase: base,
-        });
+        if (this.functionMap[fnName]) {
+          const base = this.memory.pushFrame(
+            this.invocation.opPtr,
+            operation.nArgs,
+            this.functionMap[fnName].nVars
+          );
+          this.executionStack.push({
+            function: fnName,
+            opPtr: 0,
+            nArgs: operation.nArgs,
+            frameBase: base,
+          });
+        } else if (VM_BUILTINS[fnName]) {
+          const ret = VM_BUILTINS[fnName](this.memory);
+          const sp = this.memory.SP - operation.nArgs;
+          this.memory.set(sp, ret);
+          this.memory.SP = sp + 1;
+        }
         break;
       }
       case "return": {

From c9e68b52ef8e51b1635b50f5fa677a0c83430ab5 Mon Sep 17 00:00:00 2001
From: David Souther <davidsouther+github@gmail.com>
Date: Thu, 18 Jan 2024 08:31:56 -0500
Subject: [PATCH 2/2] Unused import

---
 simulator/src/vm/vm.ts | 1 -
 1 file changed, 1 deletion(-)

diff --git a/simulator/src/vm/vm.ts b/simulator/src/vm/vm.ts
index ec7f2b4e5..93ec6df5e 100644
--- a/simulator/src/vm/vm.ts
+++ b/simulator/src/vm/vm.ts
@@ -9,7 +9,6 @@ import { FunctionInstruction, VmInstruction } from "../languages/vm.js";
 import { VmMemory } from "./memory.js";
 import { MemoryAdapter, RAM } from "../cpu/memory.js";
 import { VM_BUILTINS } from "./builtins.js";
-import { op } from "../util/asm.js";
 
 export type VmOperation =
   | FunctionOperation