feat: add I32LEB128

types/array/array.ts

@@ -57,6 +57,6 @@ export class ArrayType<T> implements SizedType<T[]>, ViewableType<T[]> {
       });
     }
 
-    return array as T[];
+    return array;
   }
 }

types/string/fixed_length.ts

@@ -12,14 +12,22 @@ export class FixedLengthString implements SizedType<string> {
 
   read(dataView: DataView, byteOffset = 0): string {
     return decoder.decode(
-      new Uint8Array(dataView.buffer, byteOffset, byteOffset + this.byteLength),
+      new Uint8Array(
+        dataView.buffer,
+        dataView.byteOffset + byteOffset,
+        this.byteLength - byteOffset,
+      ),
     );
   }
 
   write(value: string, dataView: DataView, byteOffset = 0) {
     encoder.encodeInto(
       value,
-      new Uint8Array(dataView.buffer, byteOffset, this.byteLength),
+      new Uint8Array(
+        dataView.buffer,
+        dataView.byteOffset + byteOffset,
+        this.byteLength - byteOffset,
+      ),
     );
   }
 }

types/varint/mod.ts

@@ -0,0 +1,40 @@
+import { Type } from "../types.ts";
+
+const SEGMENT_BITS = 0x7F;
+const CONTINUE_BIT = 0x80;
+
+export class Leb128Varint implements Type<number> {
+  read(dataView: DataView, byteOffset = 0): number {
+    let value = 0, position = 0;
+    while (true) {
+      const currentByte = dataView.getInt8(byteOffset);
+      value |= (currentByte & SEGMENT_BITS) << position;
+
+      if ((currentByte & CONTINUE_BIT) === 0) break;
+
+      position += 7;
+      byteOffset++;
+
+      if (position >= 32) {
+        throw new Error("VarInt is too big");
+      }
+    }
+
+    return value;
+  }
+
+  write(value: number, dataView: DataView, byteOffset = 0): void {
+    while (true) {
+      if ((value & ~SEGMENT_BITS) === 0) {
+        dataView.setInt8(byteOffset, value);
+        return;
+      }
+
+      dataView.setInt8(byteOffset, value & SEGMENT_BITS | CONTINUE_BIT);
+      byteOffset++;
+      value >>>= 7;
+    }
+  }
+}
+
+export const leb128Varint = new Leb128Varint();

types/varint/mod_test.ts

@@ -0,0 +1,70 @@
+import { Leb128Varint } from "./mod.ts";
+import { assertEquals } from "https://deno.land/[email protected]/testing/asserts.ts";
+
+Deno.test({
+  name: "Read Positive varint",
+  fn: () => {
+    let data = Uint8Array.of(127);
+    let result = new Leb128Varint().read(new DataView(data.buffer));
+    assertEquals(result, 127);
+
+    data = Uint8Array.of(128, 1);
+    result = new Leb128Varint().read(new DataView(data.buffer));
+    assertEquals(result, 128);
+
+    data = Uint8Array.of(221, 199, 1);
+    result = new Leb128Varint().read(new DataView(data.buffer));
+    assertEquals(result, 25565);
+
+    data = Uint8Array.of(255, 255, 255, 255, 7);
+    result = new Leb128Varint().read(new DataView(data.buffer));
+    assertEquals(result, 2147483647);
+  },
+});
+
+Deno.test({
+  name: "Read Negative varint",
+  fn: () => {
+    let data = Uint8Array.of(255, 255, 255, 255, 15);
+    let result = new Leb128Varint().read(new DataView(data.buffer));
+    assertEquals(result, -1);
+
+    data = Uint8Array.of(128, 128, 128, 128, 8);
+    result = new Leb128Varint().read(new DataView(data.buffer));
+    assertEquals(result, -2147483648);
+  },
+});
+
+Deno.test({
+  name: "Write Positive varint",
+  fn: () => {
+    let data = new Uint8Array(1);
+    new Leb128Varint().write(127, new DataView(data.buffer));
+    assertEquals(data, Uint8Array.of(127));
+
+    data = new Uint8Array(2);
+    new Leb128Varint().write(128, new DataView(data.buffer));
+    assertEquals(data, Uint8Array.of(128, 1));
+
+    data = new Uint8Array(3);
+    new Leb128Varint().write(25565, new DataView(data.buffer));
+    assertEquals(data, Uint8Array.of(221, 199, 1));
+
+    data = new Uint8Array(5);
+    new Leb128Varint().write(2147483647, new DataView(data.buffer));
+    assertEquals(data, Uint8Array.of(255, 255, 255, 255, 7));
+  },
+});
+
+Deno.test({
+  name: "Write Negative varint",
+  fn: () => {
+    let data = new Uint8Array(5);
+    new Leb128Varint().write(-1, new DataView(data.buffer));
+    assertEquals(data, Uint8Array.of(255, 255, 255, 255, 15));
+
+    data = new Uint8Array(5);
+    new Leb128Varint().write(-2147483648, new DataView(data.buffer));
+    assertEquals(data, Uint8Array.of(128, 128, 128, 128, 8));
+  },
+});