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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef vm_InlineCharBuffer_inl_h
+#define vm_InlineCharBuffer_inl_h
+
+#include "vm/StringType-inl.h"
+
+namespace js {
+
+template <typename CharT>
+struct MaximumInlineLength;
+
+template <>
+struct MaximumInlineLength<Latin1Char> {
+ static constexpr size_t value = JSFatInlineString::MAX_LENGTH_LATIN1;
+};
+
+template <>
+struct MaximumInlineLength<char16_t> {
+ static constexpr size_t value = JSFatInlineString::MAX_LENGTH_TWO_BYTE;
+};
+
+// Character buffer class used for ToLowerCase and ToUpperCase operations, as
+// well as other string operations where the final string length is known in
+// advance.
+//
+// Case conversion operations normally return a string with the same length as
+// the input string. To avoid over-allocation, we optimistically allocate an
+// array with same size as the input string and only when we detect special
+// casing characters, which can change the output string length, we reallocate
+// the output buffer to the final string length.
+//
+// As a further mean to improve runtime performance, the character buffer
+// contains an inline storage, so we don't need to heap-allocate an array when
+// a JSInlineString will be used for the output string.
+//
+// Why not use mozilla::Vector instead? mozilla::Vector doesn't provide enough
+// fine-grained control to avoid over-allocation when (re)allocating for exact
+// buffer sizes. This led to visible performance regressions in ยต-benchmarks.
+template <typename CharT>
+class MOZ_NON_PARAM InlineCharBuffer {
+ static constexpr size_t InlineCapacity = MaximumInlineLength<CharT>::value;
+
+ CharT inlineStorage[InlineCapacity];
+ UniquePtr<CharT[], JS::FreePolicy> heapStorage;
+
+#ifdef DEBUG
+ // In debug mode, we keep track of the requested string lengths to ensure
+ // all character buffer methods are called in the correct order and with
+ // the expected argument values.
+ size_t lastRequestedLength = 0;
+
+ void assertValidRequest(size_t expectedLastLength, size_t length) {
+ MOZ_ASSERT(length >= expectedLastLength, "cannot shrink requested length");
+ MOZ_ASSERT(lastRequestedLength == expectedLastLength);
+ lastRequestedLength = length;
+ }
+#else
+ void assertValidRequest(size_t expectedLastLength, size_t length) {}
+#endif
+
+ public:
+ CharT* get() { return heapStorage ? heapStorage.get() : inlineStorage; }
+
+ bool maybeAlloc(JSContext* cx, size_t length) {
+ assertValidRequest(0, length);
+
+ if (length <= InlineCapacity) {
+ return true;
+ }
+
+ MOZ_ASSERT(!heapStorage, "heap storage already allocated");
+ heapStorage =
+ cx->make_pod_arena_array<CharT>(js::StringBufferArena, length);
+ return !!heapStorage;
+ }
+
+ bool maybeRealloc(JSContext* cx, size_t oldLength, size_t newLength) {
+ assertValidRequest(oldLength, newLength);
+
+ if (newLength <= InlineCapacity) {
+ return true;
+ }
+
+ if (!heapStorage) {
+ heapStorage =
+ cx->make_pod_arena_array<CharT>(js::StringBufferArena, newLength);
+ if (!heapStorage) {
+ return false;
+ }
+
+ MOZ_ASSERT(oldLength <= InlineCapacity);
+ mozilla::PodCopy(heapStorage.get(), inlineStorage, oldLength);
+ return true;
+ }
+
+ CharT* oldChars = heapStorage.release();
+ CharT* newChars = cx->pod_arena_realloc(js::StringBufferArena, oldChars,
+ oldLength, newLength);
+ if (!newChars) {
+ js_free(oldChars);
+ return false;
+ }
+
+ heapStorage.reset(newChars);
+ return true;
+ }
+
+ JSString* toStringDontDeflate(JSContext* cx, size_t length,
+ js::gc::Heap heap = js::gc::Heap::Default) {
+ MOZ_ASSERT(length == lastRequestedLength);
+
+ if (JSInlineString::lengthFits<CharT>(length)) {
+ MOZ_ASSERT(
+ !heapStorage,
+ "expected only inline storage when length fits in inline string");
+
+ if (JSString* str = TryEmptyOrStaticString(cx, inlineStorage, length)) {
+ return str;
+ }
+
+ mozilla::Range<const CharT> range(inlineStorage, length);
+ return NewInlineString<CanGC>(cx, range, heap);
+ }
+
+ MOZ_ASSERT(heapStorage,
+ "heap storage was not allocated for non-inline string");
+
+ return NewStringDontDeflate<CanGC>(cx, std::move(heapStorage), length,
+ heap);
+ }
+
+ JSString* toString(JSContext* cx, size_t length,
+ js::gc::Heap heap = js::gc::Heap::Default) {
+ MOZ_ASSERT(length == lastRequestedLength);
+
+ if (JSInlineString::lengthFits<CharT>(length)) {
+ MOZ_ASSERT(
+ !heapStorage,
+ "expected only inline storage when length fits in inline string");
+
+ return NewStringCopyN<CanGC>(cx, inlineStorage, length, heap);
+ }
+
+ MOZ_ASSERT(heapStorage,
+ "heap storage was not allocated for non-inline string");
+
+ return NewString<CanGC>(cx, std::move(heapStorage), length, heap);
+ }
+};
+
+} /* namespace js */
+
+#endif /* vm_InlineCharBuffer_inl_h */