Repo created

TMessagesProj/jni/voip/webrtc/base/strings/strcat.cc

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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 "base/strings/strcat.h"
+
+namespace base {
+
+namespace {
+
+// Reserves an additional amount of capacity in the given string, growing by at
+// least 2x if necessary. Used by StrAppendT().
+//
+// The "at least 2x" growing rule duplicates the exponential growth of
+// std::string. The problem is that most implementations of reserve() will grow
+// exactly to the requested amount instead of exponentially growing like would
+// happen when appending normally. If we didn't do this, an append after the
+// call to StrAppend() would definitely cause a reallocation, and loops with
+// StrAppend() calls would have O(n^2) complexity to execute. Instead, we want
+// StrAppend() to have the same semantics as std::string::append().
+template <typename String>
+void ReserveAdditionalIfNeeded(String* str,
+                               typename String::size_type additional) {
+  const size_t required = str->size() + additional;
+  // Check whether we need to reserve additional capacity at all.
+  if (required <= str->capacity())
+    return;
+
+  str->reserve(std::max(required, str->capacity() * 2));
+}
+
+template <typename DestString, typename InputString>
+void StrAppendT(DestString* dest, span<const InputString> pieces) {
+  size_t additional_size = 0;
+  for (const auto& cur : pieces)
+    additional_size += cur.size();
+  ReserveAdditionalIfNeeded(dest, additional_size);
+
+  for (const auto& cur : pieces)
+    dest->append(cur.data(), cur.size());
+}
+
+}  // namespace
+
+std::string StrCat(span<const StringPiece> pieces) {
+  std::string result;
+  StrAppendT(&result, pieces);
+  return result;
+}
+
+string16 StrCat(span<const StringPiece16> pieces) {
+  string16 result;
+  StrAppendT(&result, pieces);
+  return result;
+}
+
+std::string StrCat(span<const std::string> pieces) {
+  std::string result;
+  StrAppendT(&result, pieces);
+  return result;
+}
+
+string16 StrCat(span<const string16> pieces) {
+  string16 result;
+  StrAppendT(&result, pieces);
+  return result;
+}
+
+void StrAppend(std::string* dest, span<const StringPiece> pieces) {
+  StrAppendT(dest, pieces);
+}
+
+void StrAppend(string16* dest, span<const StringPiece16> pieces) {
+  StrAppendT(dest, pieces);
+}
+
+void StrAppend(std::string* dest, span<const std::string> pieces) {
+  StrAppendT(dest, pieces);
+}
+
+void StrAppend(string16* dest, span<const string16> pieces) {
+  StrAppendT(dest, pieces);
+}
+
+}  // namespace base