src/third_party/v8/src/builtins/string-substring.tq

// Copyright 2019 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 string {

// ES6 #sec-string.prototype.substring
transitioning javascript builtin StringPrototypeSubstring(
    js-implicit context: NativeContext, receiver: JSAny)(...arguments): String {
  // Check that {receiver} is coercible to Object and convert it to a String.
  const string: String = ToThisString(receiver, 'String.prototype.substring');
  const length: uintptr = string.length_uintptr;

  // Conversion and bounds-checks for {start}.
  const arg0 = arguments[0];
  let start: uintptr = arg0 != Undefined ? ClampToIndexRange(arg0, length) : 0;

  // Conversion and bounds-checks for {end}.
  const arg1 = arguments[1];
  let end: uintptr =
      arg1 != Undefined ? ClampToIndexRange(arg1, length) : length;
  if (end < start) {
    const tmp: uintptr = end;
    end = start;
    start = tmp;
  }
  return SubString(string, start, end);
}
}