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// 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 {
// String.prototype.substr ( start, length )
// ES6 #sec-string.prototype.substr
transitioning javascript builtin StringPrototypeSubstr(
js-implicit context: NativeContext, receiver: JSAny)(...arguments): String {
const methodName: constexpr string = 'String.prototype.substr';
// 1. Let O be ? RequireObjectCoercible(this value).
// 2. Let S be ? ToString(O).
const string: String = ToThisString(receiver, methodName);
// 5. Let size be the number of code units in S.
const size: uintptr = string.length_uintptr;
// 3. Let intStart be ? ToInteger(start).
// 6. If intStart < 0, set intStart to max(size + intStart, 0).
const start = arguments[0];
const initStart: uintptr =
start != Undefined ? ConvertToRelativeIndex(start, size) : 0;
// 4. If length is undefined,
// let end be +∞; otherwise let end be ? ToInteger(length).
// 7. Let resultLength be min(max(end, 0), size - intStart).
const length = arguments[1];
const lengthLimit = size - initStart;
assert(lengthLimit <= size);
const resultLength: uintptr = length != Undefined ?
ClampToIndexRange(length, lengthLimit) :
lengthLimit;
// 8. If resultLength ≤ 0, return the empty String "".
if (resultLength == 0) return EmptyStringConstant();
// 9. Return the String value containing resultLength consecutive code units
// from S beginning with the code unit at index intStart.
return SubString(string, initStart, initStart + resultLength);
}
}
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