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// Copyright 2017 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include "absl/strings/str_cat.h"
#include <assert.h>
#include <cstddef>
#include <cstdint>
#include <cstring>
#include <initializer_list>
#include <limits>
#include <string>
#include "absl/base/config.h"
#include "absl/base/internal/raw_logging.h"
#include "absl/base/nullability.h"
#include "absl/strings/internal/resize_uninitialized.h"
#include "absl/strings/string_view.h"
namespace absl {
ABSL_NAMESPACE_BEGIN
// ----------------------------------------------------------------------
// StrCat()
// This merges the given strings or integers, with no delimiter. This
// is designed to be the fastest possible way to construct a string out
// of a mix of raw C strings, string_views, strings, and integer values.
// ----------------------------------------------------------------------
namespace {
// Append is merely a version of memcpy that returns the address of the byte
// after the area just overwritten.
inline absl::Nonnull<char*> Append(absl::Nonnull<char*> out,
const AlphaNum& x) {
// memcpy is allowed to overwrite arbitrary memory, so doing this after the
// call would force an extra fetch of x.size().
char* after = out + x.size();
if (x.size() != 0) {
memcpy(out, x.data(), x.size());
}
return after;
}
inline void STLStringAppendUninitializedAmortized(std::string* dest,
size_t to_append) {
strings_internal::AppendUninitializedTraits<std::string>::Append(dest,
to_append);
}
} // namespace
std::string StrCat(const AlphaNum& a, const AlphaNum& b) {
std::string result;
// Use uint64_t to prevent size_t overflow. We assume it is not possible for
// in memory strings to overflow a uint64_t.
constexpr uint64_t kMaxSize = uint64_t{std::numeric_limits<size_t>::max()};
const uint64_t result_size =
static_cast<uint64_t>(a.size()) + static_cast<uint64_t>(b.size());
ABSL_INTERNAL_CHECK(result_size <= kMaxSize, "size_t overflow");
absl::strings_internal::STLStringResizeUninitialized(
&result, static_cast<size_t>(result_size));
char* const begin = &result[0];
char* out = begin;
out = Append(out, a);
out = Append(out, b);
assert(out == begin + result.size());
return result;
}
std::string StrCat(const AlphaNum& a, const AlphaNum& b, const AlphaNum& c) {
std::string result;
// Use uint64_t to prevent size_t overflow. We assume it is not possible for
// in memory strings to overflow a uint64_t.
constexpr uint64_t kMaxSize = uint64_t{std::numeric_limits<size_t>::max()};
const uint64_t result_size = static_cast<uint64_t>(a.size()) +
static_cast<uint64_t>(b.size()) +
static_cast<uint64_t>(c.size());
ABSL_INTERNAL_CHECK(result_size <= kMaxSize, "size_t overflow");
strings_internal::STLStringResizeUninitialized(
&result, static_cast<size_t>(result_size));
char* const begin = &result[0];
char* out = begin;
out = Append(out, a);
out = Append(out, b);
out = Append(out, c);
assert(out == begin + result.size());
return result;
}
std::string StrCat(const AlphaNum& a, const AlphaNum& b, const AlphaNum& c,
const AlphaNum& d) {
std::string result;
// Use uint64_t to prevent size_t overflow. We assume it is not possible for
// in memory strings to overflow a uint64_t.
constexpr uint64_t kMaxSize = uint64_t{std::numeric_limits<size_t>::max()};
const uint64_t result_size = static_cast<uint64_t>(a.size()) +
static_cast<uint64_t>(b.size()) +
static_cast<uint64_t>(c.size()) +
static_cast<uint64_t>(d.size());
ABSL_INTERNAL_CHECK(result_size <= kMaxSize, "size_t overflow");
strings_internal::STLStringResizeUninitialized(
&result, static_cast<size_t>(result_size));
char* const begin = &result[0];
char* out = begin;
out = Append(out, a);
out = Append(out, b);
out = Append(out, c);
out = Append(out, d);
assert(out == begin + result.size());
return result;
}
namespace strings_internal {
// Do not call directly - these are not part of the public API.
std::string CatPieces(std::initializer_list<absl::string_view> pieces) {
std::string result;
// Use uint64_t to prevent size_t overflow. We assume it is not possible for
// in memory strings to overflow a uint64_t.
constexpr uint64_t kMaxSize = uint64_t{std::numeric_limits<size_t>::max()};
uint64_t total_size = 0;
for (absl::string_view piece : pieces) {
total_size += piece.size();
}
ABSL_INTERNAL_CHECK(total_size <= kMaxSize, "size_t overflow");
strings_internal::STLStringResizeUninitialized(
&result, static_cast<size_t>(total_size));
char* const begin = &result[0];
char* out = begin;
for (absl::string_view piece : pieces) {
const size_t this_size = piece.size();
if (this_size != 0) {
memcpy(out, piece.data(), this_size);
out += this_size;
}
}
assert(out == begin + result.size());
return result;
}
// It's possible to call StrAppend with an absl::string_view that is itself a
// fragment of the string we're appending to. However the results of this are
// random. Therefore, check for this in debug mode. Use unsigned math so we
// only have to do one comparison. Note, there's an exception case: appending an
// empty string is always allowed.
#define ASSERT_NO_OVERLAP(dest, src) \
assert(((src).size() == 0) || \
(uintptr_t((src).data() - (dest).data()) > uintptr_t((dest).size())))
void AppendPieces(absl::Nonnull<std::string*> dest,
std::initializer_list<absl::string_view> pieces) {
size_t old_size = dest->size();
size_t to_append = 0;
for (absl::string_view piece : pieces) {
ASSERT_NO_OVERLAP(*dest, piece);
to_append += piece.size();
}
STLStringAppendUninitializedAmortized(dest, to_append);
char* const begin = &(*dest)[0];
char* out = begin + old_size;
for (absl::string_view piece : pieces) {
const size_t this_size = piece.size();
if (this_size != 0) {
memcpy(out, piece.data(), this_size);
out += this_size;
}
}
assert(out == begin + dest->size());
}
} // namespace strings_internal
void StrAppend(absl::Nonnull<std::string*> dest, const AlphaNum& a) {
ASSERT_NO_OVERLAP(*dest, a);
std::string::size_type old_size = dest->size();
STLStringAppendUninitializedAmortized(dest, a.size());
char* const begin = &(*dest)[0];
char* out = begin + old_size;
out = Append(out, a);
assert(out == begin + dest->size());
}
void StrAppend(absl::Nonnull<std::string*> dest, const AlphaNum& a,
const AlphaNum& b) {
ASSERT_NO_OVERLAP(*dest, a);
ASSERT_NO_OVERLAP(*dest, b);
std::string::size_type old_size = dest->size();
STLStringAppendUninitializedAmortized(dest, a.size() + b.size());
char* const begin = &(*dest)[0];
char* out = begin + old_size;
out = Append(out, a);
out = Append(out, b);
assert(out == begin + dest->size());
}
void StrAppend(absl::Nonnull<std::string*> dest, const AlphaNum& a,
const AlphaNum& b, const AlphaNum& c) {
ASSERT_NO_OVERLAP(*dest, a);
ASSERT_NO_OVERLAP(*dest, b);
ASSERT_NO_OVERLAP(*dest, c);
std::string::size_type old_size = dest->size();
STLStringAppendUninitializedAmortized(dest, a.size() + b.size() + c.size());
char* const begin = &(*dest)[0];
char* out = begin + old_size;
out = Append(out, a);
out = Append(out, b);
out = Append(out, c);
assert(out == begin + dest->size());
}
void StrAppend(absl::Nonnull<std::string*> dest, const AlphaNum& a,
const AlphaNum& b, const AlphaNum& c, const AlphaNum& d) {
ASSERT_NO_OVERLAP(*dest, a);
ASSERT_NO_OVERLAP(*dest, b);
ASSERT_NO_OVERLAP(*dest, c);
ASSERT_NO_OVERLAP(*dest, d);
std::string::size_type old_size = dest->size();
STLStringAppendUninitializedAmortized(
dest, a.size() + b.size() + c.size() + d.size());
char* const begin = &(*dest)[0];
char* out = begin + old_size;
out = Append(out, a);
out = Append(out, b);
out = Append(out, c);
out = Append(out, d);
assert(out == begin + dest->size());
}
ABSL_NAMESPACE_END
} // namespace absl
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