src/third_party/v8/src/builtins/array-copywithin.tq

// Copyright 2018 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

namespace array {
macro ConvertToRelativeIndex(index: Number, length: Number): Number {
  return index < 0 ? Max(index + length, 0) : Min(index, length);
}

// https://tc39.github.io/ecma262/#sec-array.prototype.copyWithin
transitioning javascript builtin ArrayPrototypeCopyWithin(
    js-implicit context: NativeContext, receiver: JSAny)(...arguments): JSAny {
  // 1. Let O be ? ToObject(this value).
  const object: JSReceiver = ToObject_Inline(context, receiver);

  // 2. Let len be ? ToLength(? Get(O, "length")).
  const length: Number = GetLengthProperty(object);

  // 3. Let relativeTarget be ? ToInteger(target).
  const relativeTarget: Number = ToInteger_Inline(arguments[0]);

  // 4. If relativeTarget < 0, let to be max((len + relativeTarget), 0);
  //    else let to be min(relativeTarget, len).
  let to: Number = ConvertToRelativeIndex(relativeTarget, length);

  // 5. Let relativeStart be ? ToInteger(start).
  const relativeStart: Number = ToInteger_Inline(arguments[1]);

  // 6. If relativeStart < 0, let from be max((len + relativeStart), 0);
  //    else let from be min(relativeStart, len).
  let from: Number = ConvertToRelativeIndex(relativeStart, length);

  // 7. If end is undefined, let relativeEnd be len;
  //    else let relativeEnd be ? ToInteger(end).
  let relativeEnd: Number = length;
  if (arguments[2] != Undefined) {
    relativeEnd = ToInteger_Inline(arguments[2]);
  }

  // 8. If relativeEnd < 0, let final be max((len + relativeEnd), 0);
  //    else let final be min(relativeEnd, len).
  const final: Number = ConvertToRelativeIndex(relativeEnd, length);

  // 9. Let count be min(final-from, len-to).
  let count: Number = Min(final - from, length - to);

  // 10. If from<to and to<from+count, then.
  let direction: Number = 1;

  if (from < to && to < (from + count)) {
    // a. Let direction be -1.
    direction = -1;

    // b. Let from be from + count - 1.
    from = from + count - 1;

    // c. Let to be to + count - 1.
    to = to + count - 1;
  }

  // 12. Repeat, while count > 0.
  while (count > 0) {
    // a. Let fromKey be ! ToString(from).
    // b. Let toKey be ! ToString(to).
    // c. Let fromPresent be ? HasProperty(O, fromKey).
    const fromPresent: Boolean = HasProperty(object, from);

    // d. If fromPresent is true, then.
    if (fromPresent == True) {
      // i. Let fromVal be ? Get(O, fromKey).
      const fromVal: JSAny = GetProperty(object, from);

      // ii. Perform ? Set(O, toKey, fromVal, true).
      SetProperty(object, to, fromVal);
    } else {
      // i. Perform ? DeletePropertyOrThrow(O, toKey).
      DeleteProperty(object, to, LanguageMode::kStrict);
    }

    // f. Let from be from + direction.
    from = from + direction;

    // g. Let to be to + direction.
    to = to + direction;

    // h. Let count be count - 1.
    --count;
  }

  // 13. Return O.
  return object;
}
}