memoffset/lib.rs
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//! assert_eq!(offset_of!(HelpMeIAmTrappedInAStructFactory, a), 15);
36//! assert_eq!(span_of!(HelpMeIAmTrappedInAStructFactory, a), 15..19);
37//! assert_eq!(span_of!(HelpMeIAmTrappedInAStructFactory, help_me_before_they_ .. a), 0..15);
38//! ```
39//!
40//! This functionality can be useful, for example, for checksum calculations:
41//!
42//! ```ignore
43//! #[repr(C, packed)]
44//! struct Message {
45//! header: MessageHeader,
46//! fragment_index: u32,
47//! fragment_count: u32,
48//! payload: [u8; 1024],
49//! checksum: u16
50//! }
51//!
52//! let checksum_range = &raw[span_of!(Message, header..checksum)];
53//! let checksum = crc16(checksum_range);
54//! ```
55
56#![no_std]
57
58#[macro_use]
59#[cfg(doctests)]
60#[cfg(doctest)]
61extern crate doc_comment;
62#[cfg(doctests)]
63#[cfg(doctest)]
64doctest!("../README.md");
65
66/// Hidden module for things the macros need to access.
67#[doc(hidden)]
68pub mod __priv {
69 #[doc(hidden)]
70 pub use core::mem;
71 #[doc(hidden)]
72 pub use core::ptr;
73
74 /// Use type inference to obtain the size of the pointee (without actually using the pointer).
75 #[doc(hidden)]
76 pub fn size_of_pointee<T>(_ptr: *const T) -> usize {
77 mem::size_of::<T>()
78 }
79}
80
81#[macro_use]
82mod raw_field;
83#[macro_use]
84mod offset_of;
85#[macro_use]
86mod span_of;