1// Copyright (c) 2017 Gilad Naaman
2//
3// Permission is hereby granted, free of charge, to any person obtaining a copy
4// of this software and associated documentation files (the "Software"), to deal
5// in the Software without restriction, including without limitation the rights
6// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
7// copies of the Software, and to permit persons to whom the Software is
8// furnished to do so, subject to the following conditions:
9//
10// The above copyright notice and this permission notice shall be included in all
11// copies or substantial portions of the Software.
12//
13// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
14// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
15// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
16// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
17// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
18// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
19// SOFTWARE.
20
21//! A crate used for calculating offsets of struct members and their spans.
22//!
23//! This functionality currently can not be used in compile time code such as `const` or `const fn` definitions.
24//!
25//! ## Examples
26//! ```
27//! use memoffset::{offset_of, span_of};
28//!
29//! #[repr(C, packed)]
30//! struct HelpMeIAmTrappedInAStructFactory {
31//! help_me_before_they_: [u8; 15],
32//! a: u32
33//! }
34//!
35//! fn main() {
36//! assert_eq!(offset_of!(HelpMeIAmTrappedInAStructFactory, a), 15);
37//! assert_eq!(span_of!(HelpMeIAmTrappedInAStructFactory, a), 15..19);
38//! assert_eq!(span_of!(HelpMeIAmTrappedInAStructFactory, help_me_before_they_ .. a), 0..15);
39//! }
40//! ```
41//!
42//! This functionality can be useful, for example, for checksum calculations:
43//!
44//! ```ignore
45//! #[repr(C, packed)]
46//! struct Message {
47//! header: MessageHeader,
48//! fragment_index: u32,
49//! fragment_count: u32,
50//! payload: [u8; 1024],
51//! checksum: u16
52//! }
53//!
54//! let checksum_range = &raw[span_of!(Message, header..checksum)];
55//! let checksum = crc16(checksum_range);
56//! ```
57
58#![no_std]
59#![cfg_attr(
60 all(feature = "unstable_const", not(stable_const)),
61 feature(const_ptr_offset_from)
62)]
63#![cfg_attr(feature = "unstable_const", feature(const_refs_to_cell))]
64#![cfg_attr(feature = "unstable_offset_of", feature(allow_internal_unstable))]
65
66#[macro_use]
67#[cfg(doctests)]
68#[cfg(doctest)]
69extern crate doc_comment;
70#[cfg(doctests)]
71#[cfg(doctest)]
72doctest!("../README.md");
73
74/// Hidden module for things the macros need to access.
75#[doc(hidden)]
76pub mod __priv {
77 #[doc(hidden)]
78 pub use core::mem;
79 #[doc(hidden)]
80 pub use core::ptr;
81
82 /// Use type inference to obtain the size of the pointee (without actually using the pointer).
83 #[doc(hidden)]
84 pub fn size_of_pointee<T>(_ptr: *const T) -> usize {
85 mem::size_of::<T>()
86 }
87}
88
89#[macro_use]
90mod raw_field;
91#[macro_use]
92mod offset_of;
93#[macro_use]
94mod span_of;
95