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44 lines
1.6 KiB
C++
44 lines
1.6 KiB
C++
// Copyright 2021 The Chromium Authors
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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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#ifndef BASE_CONTAINERS_SPAN_RUST_H_
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#define BASE_CONTAINERS_SPAN_RUST_H_
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#include <stdint.h>
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#include "base/containers/span.h"
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#include "base/rust_buildflags.h"
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#include "third_party/rust/cxx/v1/cxx.h"
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#if !BUILDFLAG(BUILD_RUST_BASE_CONVERSIONS)
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#error "span_rust.h included without BUILD_RUST_BASE_CONVERSIONS"
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#endif
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namespace base {
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// Create a Rust slice from a base::span.
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inline rust::Slice<const uint8_t> SpanToRustSlice(span<const uint8_t> span) {
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return rust::Slice<const uint8_t>(span.data(), span.size());
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}
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// Note to future editors: if you add code to convert from a rust::Slice to
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// a base::span, you should be aware that Rust slices (and cxx)
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// return a fabricated non-null pointer for zero-length slices, and that
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// this will likely need converting to NULL before constructing a span.
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// cxx handles the conversion from NULL to an artificial pointer
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// (specifically it uses alignof<T>) in the C++ -> Rust direction, but
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// does nothing cunning in the other direction, presumably on the
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// assumption that C++ won't access the data pointer if the length is 0.
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// But we do not think (reinterpret_cast<T*>(alignof(T)), 0) can safely
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// be stored in base::span today. The pointer arithmetic
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// rules have special cases for NULL, but otherwise it is only defined if
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// there is actually an object at the address, and there is no object at
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// alignof(T).
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// https://eel.is/c++draft/expr.add#4
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// https://eel.is/c++draft/expr.add#5
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} // namespace base
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#endif // BASE_CONTAINERS_SPAN_RUST_H_
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