Fix typed array views obtained using the loader

lib/loader/index.js

@@ -192,7 +192,7 @@ function postInstantiate(baseModule, instance) {
       ? U32[arr + ARRAY_LENGTH_OFFSET >>> 2]
       : U32[buf + SIZE_OFFSET >>> 2] >>> align;
     return getView(align, info & VAL_SIGNED, info & VAL_FLOAT)
-          .slice(buf >>>= align, buf + length);
+          .subarray(buf >>>= align, buf + length);
   }
 
   baseModule.__getArrayView = __getArrayView;
@@ -221,8 +221,7 @@ function postInstantiate(baseModule, instance) {
     const buffer = memory.buffer;
     const U32 = new Uint32Array(buffer);
     const bufPtr = U32[ptr + ARRAYBUFFERVIEW_DATASTART_OFFSET >>> 2];
-    const length = U32[bufPtr + SIZE_OFFSET >>> 2];
-    return new Type(buffer).slice(bufPtr >>> alignLog2, bufPtr + length >>> alignLog2);
+    return new Type(buffer, bufPtr, U32[bufPtr + SIZE_OFFSET >>> 2] >>> alignLog2);
   }
 
   /** Gets a view on the values of a known-to-be Int8Array in the module's memory. */

lib/loader/tests/assembly/index.ts

@@ -70,3 +70,11 @@ export const INT32ARRAY_ID = idof<Int32Array>();
 export const UINT32ARRAY_ID = idof<Uint32Array>();
 export const FLOAT32ARRAY_ID = idof<Float32Array>();
 export const ARRAYI32_ID = idof<Array<i32>>();
+
+export function newFloat32Array(size: i32): Float32Array {
+  return new Float32Array(size);
+}
+
+export function modifyFloat32Array(array: Float32Array, index: i32, value: f32): void {
+  array[index] = value;
+}

lib/loader/tests/index.js

@@ -151,3 +151,25 @@ module.__release(car); // uses Car.prototype.valueOf to obtain `thisPtr`
 
 // should be able to use trace
 module.dotrace(42);
+
+// should be able to mutate an array in place using getArrayView
+{
+  let ptr = module.__retain(module.__allocArray(module.FLOAT32ARRAY_ID, [ 1, 2, 3]));
+  let view = module.__getArrayView(ptr);
+  assert.deepEqual(view, new Float32Array([1, 2, 3]));
+  module.modifyFloat32Array(ptr, 0, 4);
+  assert.deepEqual(view, new Float32Array([4, 2, 3]));
+  module.__release(ptr);
+}
+
+// should be able to mutate an array in place using getFloat32Array
+{
+  let ptr = module.newFloat32Array(3); // returns are pre-retained
+  let view = module.__getFloat32Array(ptr);
+  assert.deepEqual(view, new Float32Array([0, 0, 0]));
+  module.modifyFloat32Array(ptr, 0, 3);
+  module.modifyFloat32Array(ptr, 1, 2);
+  module.modifyFloat32Array(ptr, 2, 1);
+  assert.deepEqual(view, new Float32Array([3, 2, 1]));
+  module.__release(ptr);
+}