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// Copyright 2017 The Chromium 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 "third_party/blink/renderer/platform/bindings/string_resource.h"
#include <type_traits>
#include "third_party/blink/renderer/platform/bindings/v8_binding.h"
namespace blink {
template <class StringClass>
struct StringTraits {
static const StringClass& FromStringResource(StringResourceBase*);
template <typename V8StringTrait>
static StringClass FromV8String(v8::Isolate*, v8::Local<v8::String>, int);
};
template <>
struct StringTraits<String> {
static const String FromStringResource(StringResourceBase* resource) {
return resource->GetWTFString();
}
template <typename V8StringTrait>
static String FromV8String(v8::Isolate*, v8::Local<v8::String>, int);
};
template <>
struct StringTraits<AtomicString> {
static const AtomicString FromStringResource(StringResourceBase* resource) {
return resource->GetAtomicString();
}
template <typename V8StringTrait>
static AtomicString FromV8String(v8::Isolate*, v8::Local<v8::String>, int);
};
struct V8StringTwoBytesTrait {
typedef UChar CharType;
ALWAYS_INLINE static void Write(v8::Isolate* isolate,
v8::Local<v8::String> v8_string,
CharType* buffer,
int length) {
v8_string->Write(isolate, reinterpret_cast<uint16_t*>(buffer), 0, length);
}
};
struct V8StringOneByteTrait {
typedef LChar CharType;
ALWAYS_INLINE static void Write(v8::Isolate* isolate,
v8::Local<v8::String> v8_string,
CharType* buffer,
int length) {
v8_string->WriteOneByte(isolate, buffer, 0, length);
}
};
template <typename V8StringTrait>
String StringTraits<String>::FromV8String(v8::Isolate* isolate,
v8::Local<v8::String> v8_string,
int length) {
DCHECK(v8_string->Length() == length);
typename V8StringTrait::CharType* buffer;
String result = String::CreateUninitialized(length, buffer);
V8StringTrait::Write(isolate, v8_string, buffer, length);
return result;
}
template <typename V8StringTrait>
AtomicString StringTraits<AtomicString>::FromV8String(
v8::Isolate* isolate,
v8::Local<v8::String> v8_string,
int length) {
DCHECK(v8_string->Length() == length);
static const int kInlineBufferSize =
32 / sizeof(typename V8StringTrait::CharType);
if (length <= kInlineBufferSize) {
typename V8StringTrait::CharType inline_buffer[kInlineBufferSize];
V8StringTrait::Write(isolate, v8_string, inline_buffer, length);
return AtomicString(inline_buffer, static_cast<unsigned>(length));
}
typename V8StringTrait::CharType* buffer;
String string = String::CreateUninitialized(length, buffer);
V8StringTrait::Write(isolate, v8_string, buffer, length);
return AtomicString(string);
}
template <typename StringType>
StringType ToBlinkString(v8::Local<v8::String> v8_string,
ExternalMode external) {
{
// This portion of this function is very hot in certain Dromeao benchmarks.
v8::String::Encoding encoding;
v8::String::ExternalStringResourceBase* resource =
v8_string->GetExternalStringResourceBase(&encoding);
if (LIKELY(!!resource)) {
// Inheritance:
// - V8 side: v8::String::ExternalStringResourceBase
// -> v8::External{One,}ByteStringResource
// - Both: StringResource{8,16}Base inherits from the matching v8 class.
static_assert(std::is_base_of<v8::String::ExternalOneByteStringResource,
StringResource8Base>::value,
"");
static_assert(std::is_base_of<v8::String::ExternalStringResource,
StringResource16Base>::value,
"");
static_assert(
std::is_base_of<StringResourceBase, StringResource8Base>::value, "");
static_assert(
std::is_base_of<StringResourceBase, StringResource16Base>::value, "");
// Then StringResource{8,16}Base allows to go from one ancestry path to
// the other one. Even though it's empty, removing it causes UB, see
// crbug.com/909796.
StringResourceBase* base;
if (encoding == v8::String::ONE_BYTE_ENCODING)
base = static_cast<StringResource8Base*>(resource);
else
base = static_cast<StringResource16Base*>(resource);
return StringTraits<StringType>::FromStringResource(base);
}
}
int length = v8_string->Length();
if (UNLIKELY(!length))
return StringType("");
v8::Isolate* isolate = v8::Isolate::GetCurrent();
bool one_byte = v8_string->ContainsOnlyOneByte();
StringType result(
one_byte ? StringTraits<StringType>::template FromV8String<
V8StringOneByteTrait>(isolate, v8_string, length)
: StringTraits<StringType>::template FromV8String<
V8StringTwoBytesTrait>(isolate, v8_string, length));
if (external != kExternalize || !v8_string->CanMakeExternal())
return result;
if (result.Is8Bit()) {
StringResource8* string_resource = new StringResource8(result);
if (UNLIKELY(!v8_string->MakeExternal(string_resource)))
delete string_resource;
} else {
StringResource16* string_resource = new StringResource16(result);
if (UNLIKELY(!v8_string->MakeExternal(string_resource)))
delete string_resource;
}
return result;
}
// Explicitly instantiate the above template with the expected
// parameterizations, to ensure the compiler generates the code; otherwise link
// errors can result in GCC 4.4.
template String ToBlinkString<String>(v8::Local<v8::String>, ExternalMode);
template AtomicString ToBlinkString<AtomicString>(v8::Local<v8::String>,
ExternalMode);
// Fast but non thread-safe version.
static String ToBlinkStringFast(int value) {
// Caching of small strings below is not thread safe: newly constructed
// AtomicString are not safely published.
DCHECK(IsMainThread());
// Most numbers used are <= 100. Even if they aren't used there's very little
// cost in using the space.
const int kLowNumbers = 100;
DEFINE_STATIC_LOCAL(Vector<AtomicString>, low_numbers, (kLowNumbers + 1));
String web_core_string;
if (0 <= value && value <= kLowNumbers) {
web_core_string = low_numbers[value];
if (!web_core_string) {
AtomicString value_string = AtomicString::Number(value);
low_numbers[value] = value_string;
web_core_string = value_string;
}
} else {
web_core_string = String::Number(value);
}
return web_core_string;
}
String ToBlinkString(int value) {
// If we are on the main thread (this should always true for non-workers),
// call the faster one.
if (IsMainThread())
return ToBlinkStringFast(value);
return String::Number(value);
}
} // namespace blink
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