path: root/cpp/018address

:(scenario "copy_indirect")
# Instructions can read from addresses pointing at other locations using the 'deref' property.
recipe main [
  1:address:integer <- copy 2:literal
  2:integer <- copy 34:literal
  # This loads location 1 as an address and looks up *that* location.
  3:integer <- copy 1:address:integer/deref
]
+run: instruction 2
+mem: location 1 is 2
+mem: location 2 is 34
+mem: storing in location 3

:(replace{} "vector<int> read_memory(reagent x)")
vector<int> read_memory(reagent x) {
  vector<int> result;
  if (x.types[0] == 0) {  // literal
    result.push_back(to_int(x.name));
    return result;
  }
  x = canonize(x);
  int base = to_int(x.name);
  for (size_t offset = 0; offset < Type[x.types[0]].size; ++offset) {
    int val = Memory[base+offset];
    trace("mem") << "location " << base+offset << " is " << val;
    result.push_back(val);
  }
  return result;
}

:(replace{} "void write_memory(reagent x, vector<int> data)")
void write_memory(reagent x, vector<int> data) {
  int base = to_int(x.name);
  size_t size = size_of(x.types[0]);
  if (size != data.size()) raise << "size mismatch in storing to " << x.to_string();
  for (size_t offset = 0; offset < size; ++offset) {
    trace("mem") << "storing in location " << base+offset;
    Memory[base+offset] = data[offset];
  }
}

:(code)
reagent canonize(reagent x) {
  reagent r = x;
  while (has_property(r, "deref"))
    r = deref(r);
  return r;
}

bool has_property(reagent x, string name) {
  for (size_t i = 0; i < x.properties.size(); ++i) {
    if (x.properties[i].first == name) return true;
  }
  return false;
}

reagent deref(reagent x) {
  reagent result("");
  assert(x.types[0] == 2);  // address

  // compute name
  ostringstream out;
  out << Memory[to_int(x.name)];
  result.name = out.str();
  trace("mem") << "location " << x.name << " is " << result.name;

  // populate types
  copy(++x.types.begin(), x.types.end(), inserter(result.types, result.types.begin()));

  // drop-one 'deref'
  int i = 0;
  int len = x.properties.size();
  while (true) {
    assert(i < len);
    if (x.properties[i].first == "deref") break;
    result.properties.push_back(x.properties[i]);
    ++i;
  }
  ++i;  // skip first deref
  while (i < len) {
    result.properties.push_back(x.properties[i]);
  }
  return result;
}