memoffset/
span_of.rs

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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/// Reexport for `local_inner_macros`; see
22/// <https://doc.rust-lang.org/edition-guide/rust-2018/macros/macro-changes.html#macros-using-local_inner_macros>.
23#[doc(hidden)]
24#[macro_export]
25macro_rules! _memoffset__compile_error {
26    ($($inner:tt)*) => {
27        compile_error! { $($inner)* }
28    }
29}
30
31/// Produces a range instance representing the sub-slice containing the specified member.
32///
33/// This macro provides 2 forms of differing functionalities.
34///
35/// The first form is identical to the appearance of the `offset_of!` macro.
36///
37/// ```ignore
38/// span_of!(Struct, member)
39/// ```
40///
41/// The second form of `span_of!` returns a sub-slice which starts at one field, and ends at another.
42/// The general pattern of this form is:
43///
44/// ```ignore
45/// // Exclusive
46/// span_of!(Struct, member_a .. member_b)
47/// // Inclusive
48/// span_of!(Struct, member_a ..= member_b)
49///
50/// // Open-ended ranges
51/// span_of!(Struct, .. end)
52/// span_of!(Struct, start ..)
53/// ```
54///
55/// ### Note
56/// This macro uses recursion in order to resolve the range expressions, so there is a limit to
57/// the complexity of the expression.
58/// In order to raise the limit, the compiler's recursion limit should be lifted.
59///
60/// ### Safety
61/// The inter-field form mentioned above assumes that the first field is positioned before the
62/// second.
63/// This is only guaranteed for `repr(C)` structs.
64/// Usage with `repr(Rust)` structs may yield unexpected results, like downward-going ranges,
65/// spans that include unexpected fields, empty spans, or spans that include *unexpected* padding bytes.
66///
67/// ## Examples
68/// ```
69/// use memoffset::span_of;
70///
71/// #[repr(C)]
72/// struct Florp {
73///     a: u32
74/// }
75///
76/// #[repr(C)]
77/// struct Blarg {
78///     x: [u32; 2],
79///     y: [u8; 56],
80///     z: Florp,
81///     egg: [[u8; 4]; 4]
82/// }
83///
84/// assert_eq!(0..84,  span_of!(Blarg, ..));
85/// assert_eq!(0..8,   span_of!(Blarg, .. y));
86/// assert_eq!(0..64,  span_of!(Blarg, ..= y));
87/// assert_eq!(0..8,   span_of!(Blarg, x));
88/// assert_eq!(8..84,  span_of!(Blarg, y ..));
89/// assert_eq!(0..8,   span_of!(Blarg, x .. y));
90/// assert_eq!(0..64,  span_of!(Blarg, x ..= y));
91/// ```
92#[macro_export(local_inner_macros)]
93macro_rules! span_of {
94    (@helper  $root:ident, [] ..=) => {
95        _memoffset__compile_error!("Expected a range, found '..='")
96    };
97    (@helper $root:ident, [] ..) => {
98        _memoffset__compile_error!("Expected a range, found '..'")
99    };
100    // No explicit begin for range.
101    (@helper $root:ident, $parent:path, [] ..) => {{
102        ($root as usize,
103         $root as usize + $crate::__priv::size_of_pointee($root))
104    }};
105    (@helper $root:ident, $parent:path, [] ..= $end:tt) => {{
106        let end = raw_field!($root, $parent, $end);
107        ($root as usize, end as usize + $crate::__priv::size_of_pointee(end))
108    }};
109    (@helper $root:ident, $parent:path, [] .. $end:tt) => {{
110        ($root as usize, raw_field!($root, $parent, $end) as usize)
111    }};
112    // Explicit begin and end for range.
113    (@helper $root:ident, $parent:path, # $begin:tt [] ..= $end:tt) => {{
114        let begin = raw_field!($root, $parent, $begin);
115        let end = raw_field!($root, $parent, $end);
116        (begin as usize, end as usize + $crate::__priv::size_of_pointee(end))
117    }};
118    (@helper $root:ident, $parent:path, # $begin:tt [] .. $end:tt) => {{
119        (raw_field!($root, $parent, $begin) as usize,
120         raw_field!($root, $parent, $end) as usize)
121    }};
122    // No explicit end for range.
123    (@helper $root:ident, $parent:path, # $begin:tt [] ..) => {{
124        (raw_field!($root, $parent, $begin) as usize,
125         $root as usize + $crate::__priv::size_of_pointee($root))
126    }};
127    (@helper $root:ident, $parent:path, # $begin:tt [] ..=) => {{
128        _memoffset__compile_error!(
129            "Found inclusive range to the end of a struct. Did you mean '..' instead of '..='?")
130    }};
131    // Just one field.
132    (@helper $root:ident, $parent:path, # $field:tt []) => {{
133        let field = raw_field!($root, $parent, $field);
134        (field as usize, field as usize + $crate::__priv::size_of_pointee(field))
135    }};
136    // Parsing.
137    (@helper $root:ident, $parent:path, $(# $begin:tt)+ [] $tt:tt $($rest:tt)*) => {{
138        span_of!(@helper $root, $parent, $(#$begin)* #$tt [] $($rest)*)
139    }};
140    (@helper $root:ident, $parent:path, [] $tt:tt $($rest:tt)*) => {{
141        span_of!(@helper $root, $parent, #$tt [] $($rest)*)
142    }};
143
144    // Entry point.
145    ($sty:path, $($exp:tt)+) => ({
146        // Get a base pointer.
147        _memoffset__let_base_ptr!(root, $sty);
148        let base = root as usize;
149        let (begin, end) = span_of!(@helper root, $sty, [] $($exp)*);
150        begin-base..end-base
151    });
152}
153
154#[cfg(test)]
155mod tests {
156    use core::mem;
157
158    #[test]
159    fn span_simple() {
160        #[repr(C)]
161        struct Foo {
162            a: u32,
163            b: [u8; 2],
164            c: i64,
165        }
166
167        assert_eq!(span_of!(Foo, a), 0..4);
168        assert_eq!(span_of!(Foo, b), 4..6);
169        assert_eq!(span_of!(Foo, c), 8..8 + 8);
170    }
171
172    #[test]
173    #[cfg_attr(miri, ignore)] // this creates unaligned references
174    fn span_simple_packed() {
175        #[repr(C, packed)]
176        struct Foo {
177            a: u32,
178            b: [u8; 2],
179            c: i64,
180        }
181
182        assert_eq!(span_of!(Foo, a), 0..4);
183        assert_eq!(span_of!(Foo, b), 4..6);
184        assert_eq!(span_of!(Foo, c), 6..6 + 8);
185    }
186
187    #[test]
188    fn span_forms() {
189        #[repr(C)]
190        struct Florp {
191            a: u32,
192        }
193
194        #[repr(C)]
195        struct Blarg {
196            x: u64,
197            y: [u8; 56],
198            z: Florp,
199            egg: [[u8; 4]; 5],
200        }
201
202        // Love me some brute force
203        assert_eq!(0..8, span_of!(Blarg, x));
204        assert_eq!(64..68, span_of!(Blarg, z));
205        assert_eq!(68..mem::size_of::<Blarg>(), span_of!(Blarg, egg));
206
207        assert_eq!(8..64, span_of!(Blarg, y..z));
208        assert_eq!(0..64, span_of!(Blarg, x..=y));
209    }
210
211    #[test]
212    fn ig_test() {
213        #[repr(C)]
214        struct Member {
215            foo: u32,
216        }
217
218        #[repr(C)]
219        struct Test {
220            x: u64,
221            y: [u8; 56],
222            z: Member,
223            egg: [[u8; 4]; 4],
224        }
225
226        assert_eq!(span_of!(Test, ..x), 0..0);
227        assert_eq!(span_of!(Test, ..=x), 0..8);
228        assert_eq!(span_of!(Test, ..y), 0..8);
229        assert_eq!(span_of!(Test, ..=y), 0..64);
230        assert_eq!(span_of!(Test, ..z), 0..64);
231        assert_eq!(span_of!(Test, ..=z), 0..68);
232        assert_eq!(span_of!(Test, ..egg), 0..68);
233        assert_eq!(span_of!(Test, ..=egg), 0..84);
234        assert_eq!(span_of!(Test, ..), 0..mem::size_of::<Test>());
235        assert_eq!(
236            span_of!(Test, x..),
237            offset_of!(Test, x)..mem::size_of::<Test>()
238        );
239        assert_eq!(
240            span_of!(Test, y..),
241            offset_of!(Test, y)..mem::size_of::<Test>()
242        );
243
244        assert_eq!(
245            span_of!(Test, z..),
246            offset_of!(Test, z)..mem::size_of::<Test>()
247        );
248        assert_eq!(
249            span_of!(Test, egg..),
250            offset_of!(Test, egg)..mem::size_of::<Test>()
251        );
252        assert_eq!(
253            span_of!(Test, x..y),
254            offset_of!(Test, x)..offset_of!(Test, y)
255        );
256        assert_eq!(
257            span_of!(Test, x..=y),
258            offset_of!(Test, x)..offset_of!(Test, y) + mem::size_of::<[u8; 56]>()
259        );
260    }
261}
memoffset/span_of.rs

memoffset/
span_of.rs
