1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
|
// 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.
#include 'src/builtins/builtins-regexp-gen.h'
namespace string {
// https://tc39.github.io/ecma262/#sec-string.prototype.startswith
transitioning javascript builtin StringPrototypeStartsWith(
js-implicit context: NativeContext,
receiver: JSAny)(...arguments): Boolean {
const searchString: JSAny = arguments[0];
const position: JSAny = arguments[1];
const kBuiltinName: constexpr string = 'String.prototype.startsWith';
// 1. Let O be ? RequireObjectCoercible(this value).
// 2. Let S be ? ToString(O).
const string: String = ToThisString(receiver, kBuiltinName);
// 3. Let isRegExp be ? IsRegExp(searchString).
// 4. If isRegExp is true, throw a TypeError exception.
if (regexp::IsRegExp(searchString)) {
ThrowTypeError(MessageTemplate::kFirstArgumentNotRegExp, kBuiltinName);
}
// 5. Let searchStr be ? ToString(searchString).
const searchStr: String = ToString_Inline(searchString);
// 8. Let len be the length of S.
const len: uintptr = string.length_uintptr;
// 6. Let pos be ? ToInteger(position).
// 7. Assert: If position is undefined, then pos is 0.
// 9. Let start be min(max(pos, 0), len).
const start: uintptr =
(position != Undefined) ? ClampToIndexRange(position, len) : 0;
// 10. Let searchLength be the length of searchStr.
const searchLength: uintptr = searchStr.length_uintptr;
// 11. If searchLength + start is greater than len, return false.
// The comparison is rephrased to be overflow-friendly with unsigned
// indices.
if (searchLength > len - start) return False;
// 12. If the sequence of code units of S starting at start of length
// searchLength is the same as the full code unit sequence of searchStr,
// return true.
// 13. Otherwise, return false.
try {
// Fast Path: If both strings are direct and relevant indices are Smis.
return TryFastStringCompareSequence(string, searchStr, start, searchLength)
otherwise Slow;
} label Slow {
// Slow Path: If either of the string is indirect, bail into runtime.
return StringCompareSequence(
context, string, searchStr, Convert<Number>(start));
}
}
}
|
