mirror of
https://github.com/abseil/abseil-cpp.git
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bd6adb86c2
This associates debug information with the assertion sites, allowing clearer stack-traces for assertion failures and better accounting of the performance overhead of assertions. PiperOrigin-RevId: 910863016 Change-Id: Ic615a9eeb8ad4b3f8c035074df4ff8347190e5c7
94 lines
3.8 KiB
C++
94 lines
3.8 KiB
C++
// Copyright 2025 The Abseil Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#ifndef ABSL_STRINGS_INTERNAL_APPEND_AND_OVERWRITE_H_
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#define ABSL_STRINGS_INTERNAL_APPEND_AND_OVERWRITE_H_
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#include "absl/base/config.h"
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#include "absl/base/internal/hardening.h"
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#include "absl/base/macros.h"
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#include "absl/base/optimization.h"
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#include "absl/base/throw_delegate.h"
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#include "absl/strings/resize_and_overwrite.h"
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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namespace strings_internal {
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// An internal-only variant similar to `absl::StringResizeAndOverwrite()`
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// optimized for repeated appends to a string that uses exponential growth so
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// that the amortized complexity of increasing the string size by a small amount
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// is O(1), in contrast to O(str.size()) in the case of precise growth. Use of
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// this function is subtle; see https://reviews.llvm.org/D102727 to understand
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// the tradeoffs.
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//
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// Appends at most `append_n` characters to `str`, using the user-provided
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// operation `append_op` to modify the possibly indeterminate
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// contents. `append_op` must return the length of the buffer appended to `str`.
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//
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// Invalidates all iterators, pointers, and references into `str`, regardless
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// of whether reallocation occurs.
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//
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// `append_op(value_type* buf, size_t buf_size)` is allowed to write
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// `value_type{}` to `buf[buf_size]`, which facilitiates interoperation with
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// functions that write a trailing NUL.
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template <typename T, typename Op>
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void StringAppendAndOverwrite(T& str, typename T::size_type append_n,
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Op append_op) {
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if (ABSL_PREDICT_FALSE(append_n > str.max_size() - str.size())) {
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ThrowStdLengthError("absl::strings_internal::StringAppendAndOverwrite");
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}
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auto old_size = str.size();
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auto resize = old_size + append_n;
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if (resize > str.capacity()) {
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// Make sure to always grow by at least a factor of 2x.
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const auto min_growth = str.capacity();
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if (ABSL_PREDICT_FALSE(str.capacity() > str.max_size() - min_growth)) {
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str.reserve(str.max_size());
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} else if (resize < str.capacity() + min_growth) {
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str.reserve(str.capacity() + min_growth);
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}
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}
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// Avoid calling StringResizeAndOverwrite() here since it does an MSAN
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// verification on the entire string. StringResizeAndOverwriteImpl() is
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// StringResizeAndOverwrite() without the MSAN verification.
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StringResizeAndOverwriteImpl(
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str, resize,
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[old_size, append_n, do_append = std::move(append_op)](
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typename T::value_type* data_ptr, typename T::size_type) mutable {
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typename T::size_type num_appended = static_cast<typename T::size_type>(
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std::move(do_append)(data_ptr + old_size, append_n));
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absl::base_internal::HardeningAssertGE(num_appended,
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typename T::size_type{0});
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absl::base_internal::HardeningAssertLE(num_appended, append_n);
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return old_size + num_appended;
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});
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#if defined(ABSL_HAVE_MEMORY_SANITIZER)
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// Only check the region appended to. Checking the entire string would cause
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// pathological quadratic verfication on repeated small appends.
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__msan_check_mem_is_initialized(str.data() + old_size, str.size() - old_size);
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#endif
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}
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} // namespace strings_internal
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ABSL_NAMESPACE_END
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} // namespace absl
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#endif // ABSL_STRINGS_INTERNAL_APPEND_AND_OVERWRITE_H_
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