tendril/
buf32.rs

1// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
2// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
3// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
4// option. This file may not be copied, modified, or distributed
5// except according to those terms.
6
7//! Provides an unsafe owned buffer type, used in implementing `Tendril`.
8
9use std::{mem, ptr, slice, u32};
10
11use OFLOW;
12
13pub const MIN_CAP: u32 = 16;
14
15pub const MAX_LEN: usize = u32::MAX as usize;
16
17/// A buffer points to a header of type `H`, which is followed by `MIN_CAP` or more
18/// bytes of storage.
19pub struct Buf32<H> {
20    pub ptr: *mut H,
21    pub len: u32,
22    pub cap: u32,
23}
24
25#[inline(always)]
26fn bytes_to_vec_capacity<H>(x: u32) -> usize {
27    let header = mem::size_of::<H>();
28    debug_assert!(header > 0);
29    let x = (x as usize).checked_add(header).expect(OFLOW);
30    // Integer ceil https://stackoverflow.com/a/2745086/1162888
31    1 + ((x - 1) / header)
32}
33
34impl<H> Buf32<H> {
35    #[inline]
36    pub unsafe fn with_capacity(mut cap: u32, h: H) -> Buf32<H> {
37        if cap < MIN_CAP {
38            cap = MIN_CAP;
39        }
40
41        let mut vec = Vec::<H>::with_capacity(bytes_to_vec_capacity::<H>(cap));
42        let ptr = vec.as_mut_ptr();
43        mem::forget(vec);
44        ptr::write(ptr, h);
45
46        Buf32 {
47            ptr: ptr,
48            len: 0,
49            cap: cap,
50        }
51    }
52
53    #[inline]
54    pub unsafe fn destroy(self) {
55        mem::drop(Vec::from_raw_parts(
56            self.ptr,
57            1,
58            bytes_to_vec_capacity::<H>(self.cap),
59        ));
60    }
61
62    #[inline(always)]
63    pub unsafe fn data_ptr(&self) -> *mut u8 {
64        (self.ptr as *mut u8).offset(mem::size_of::<H>() as isize)
65    }
66
67    #[inline(always)]
68    pub unsafe fn data(&self) -> &[u8] {
69        slice::from_raw_parts(self.data_ptr(), self.len as usize)
70    }
71
72    #[inline(always)]
73    pub unsafe fn data_mut(&mut self) -> &mut [u8] {
74        slice::from_raw_parts_mut(self.data_ptr(), self.len as usize)
75    }
76
77    /// Grow the capacity to at least `new_cap`.
78    ///
79    /// This will panic if the capacity calculation overflows `u32`.
80    #[inline]
81    pub unsafe fn grow(&mut self, new_cap: u32) {
82        if new_cap <= self.cap {
83            return;
84        }
85
86        let new_cap = new_cap.checked_next_power_of_two().expect(OFLOW);
87        let mut vec = Vec::from_raw_parts(self.ptr, 0, bytes_to_vec_capacity::<H>(self.cap));
88        vec.reserve_exact(bytes_to_vec_capacity::<H>(new_cap));
89        self.ptr = vec.as_mut_ptr();
90        self.cap = new_cap;
91        mem::forget(vec);
92    }
93}
94
95#[cfg(test)]
96mod test {
97    use super::Buf32;
98    use std::ptr;
99
100    #[test]
101    fn smoke_test() {
102        unsafe {
103            let mut b = Buf32::with_capacity(0, 0u8);
104            assert_eq!(b"", b.data());
105
106            b.grow(5);
107            ptr::copy_nonoverlapping(b"Hello".as_ptr(), b.data_ptr(), 5);
108
109            assert_eq!(b"", b.data());
110            b.len = 5;
111            assert_eq!(b"Hello", b.data());
112
113            b.grow(1337);
114            assert!(b.cap >= 1337);
115            assert_eq!(b"Hello", b.data());
116
117            b.destroy();
118        }
119    }
120}
tendril/buf32.rs

tendril/
buf32.rs
