29 lines
1.3 KiB
Rust
29 lines
1.3 KiB
Rust
// Copyright 2013-2016 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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// Private macro to get the offset of a struct field in bytes from the address of the struct.
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macro_rules! offset_of {
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($container:path, $field:ident) => {{
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// Make sure the field actually exists. This line ensures that a compile-time error is
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// generated if $field is accessed through a Deref impl.
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let $container { $field : _, .. };
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// Create an (invalid) instance of the container and calculate the offset to its
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// field. Using a null pointer might be UB if `&(*(0 as *const T)).field` is interpreted to
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// be nullptr deref.
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let invalid: $container = ::core::mem::uninitialized();
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let offset = &invalid.$field as *const _ as usize - &invalid as *const _ as usize;
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// Do not run destructors on the made up invalid instance.
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::core::mem::forget(invalid);
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offset as isize
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}};
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}
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