86 lines
2.5 KiB
C++
86 lines
2.5 KiB
C++
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// Copyright 2017 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#include "base/strings/strcat.h"
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namespace base {
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namespace {
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// Reserves an additional amount of capacity in the given string, growing by at
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// least 2x if necessary. Used by StrAppendT().
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//
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// The "at least 2x" growing rule duplicates the exponential growth of
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// std::string. The problem is that most implementations of reserve() will grow
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// exactly to the requested amount instead of exponentially growing like would
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// happen when appending normally. If we didn't do this, an append after the
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// call to StrAppend() would definitely cause a reallocation, and loops with
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// StrAppend() calls would have O(n^2) complexity to execute. Instead, we want
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// StrAppend() to have the same semantics as std::string::append().
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template <typename String>
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void ReserveAdditionalIfNeeded(String* str,
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typename String::size_type additional) {
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const size_t required = str->size() + additional;
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// Check whether we need to reserve additional capacity at all.
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if (required <= str->capacity())
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return;
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str->reserve(std::max(required, str->capacity() * 2));
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}
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template <typename DestString, typename InputString>
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void StrAppendT(DestString* dest, span<const InputString> pieces) {
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size_t additional_size = 0;
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for (const auto& cur : pieces)
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additional_size += cur.size();
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ReserveAdditionalIfNeeded(dest, additional_size);
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for (const auto& cur : pieces)
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dest->append(cur.data(), cur.size());
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}
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} // namespace
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std::string StrCat(span<const StringPiece> pieces) {
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std::string result;
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StrAppendT(&result, pieces);
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return result;
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}
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string16 StrCat(span<const StringPiece16> pieces) {
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string16 result;
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StrAppendT(&result, pieces);
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return result;
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}
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std::string StrCat(span<const std::string> pieces) {
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std::string result;
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StrAppendT(&result, pieces);
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return result;
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}
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string16 StrCat(span<const string16> pieces) {
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string16 result;
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StrAppendT(&result, pieces);
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return result;
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}
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void StrAppend(std::string* dest, span<const StringPiece> pieces) {
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StrAppendT(dest, pieces);
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}
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void StrAppend(string16* dest, span<const StringPiece16> pieces) {
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StrAppendT(dest, pieces);
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}
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void StrAppend(std::string* dest, span<const std::string> pieces) {
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StrAppendT(dest, pieces);
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}
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void StrAppend(string16* dest, span<const string16> pieces) {
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StrAppendT(dest, pieces);
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}
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} // namespace base
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