magnetic/buffer/
dynamic.rs

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
//! Buffer which is allocated at run time

use super::Buffer;
use crate::util::{alloc, dealloc};

/// Holds data allocated from the heap at run time
pub struct DynamicBuffer<T> {
    ptr: *mut T,
    size: usize,
}

impl<T> DynamicBuffer<T> {
    /// Create a new `DynamicBuffer` of the given size. This method will
    /// return an error if the requested number of bytes could not be
    /// allocated.
    pub fn new(size: usize) -> Result<Self, &'static str> {
        if size > 0 {
            Ok(DynamicBuffer {
                ptr: alloc(size),
                size,
            })
        } else {
            Err("Buffer size must be greater than 0")
        }
    }
}

impl<T> Drop for DynamicBuffer<T> {
    fn drop(&mut self) {
        dealloc(self.ptr, self.size);
    }
}

unsafe impl<T: Send> Send for DynamicBuffer<T> {}

impl<T> Buffer<T> for DynamicBuffer<T> {
    #[inline(always)]
    fn size(&self) -> usize {
        self.size
    }

    #[inline(always)]
    fn at(&self, idx: usize) -> *const T {
        let idx = idx % self.size;
        unsafe { self.ptr.add(idx) }
    }

    fn at_mut(&mut self, idx: usize) -> *mut T {
        let idx = idx % self.size;
        unsafe { self.ptr.add(idx) }
    }
}

/// Holds data allocated from the heap at run time. Similar to `DynamicBuffer`
/// except that the size must be a power of two. This will result in slightly
/// faster runtime performance due to the use of a mask instead of modulus
/// when computing buffer indexes.
pub struct DynamicBufferP2<T> {
    ptr: *mut T,
    mask: usize,
}

impl<T> DynamicBufferP2<T> {
    /// Create a new `DynamicBufferP2` of the given size. This method will
    /// return an error if the requested number of bytes could not be
    /// allocated or size is not a power of two.
    pub fn new(size: usize) -> Result<Self, &'static str> {
        match size {
            0 => Err("Buffer size must be greater than 0"),
            _ if ((size - 1) & size) == 0 => Ok(DynamicBufferP2 {
                ptr: alloc(size),
                mask: size - 1,
            }),
            _ => Err("Buffer size must be a power of two"),
        }
    }
}

impl<T> Drop for DynamicBufferP2<T> {
    fn drop(&mut self) {
        dealloc(self.ptr, self.mask + 1);
    }
}

unsafe impl<T: Send> Send for DynamicBufferP2<T> {}

impl<T> Buffer<T> for DynamicBufferP2<T> {
    #[inline(always)]
    fn size(&self) -> usize {
        self.mask + 1
    }

    #[inline(always)]
    fn at(&self, idx: usize) -> *const T {
        let idx = idx & self.mask;
        unsafe { self.ptr.add(idx) }
    }

    #[inline(always)]
    fn at_mut(&mut self, idx: usize) -> *mut T {
        let idx = idx & self.mask;
        unsafe { self.ptr.add(idx) }
    }
}

#[cfg(test)]
mod test {
    use super::super::Buffer;
    use super::*;

    #[test]
    fn bad_buf() {
        assert!(DynamicBuffer::<u8>::new(0).is_err());
        assert!(DynamicBufferP2::<u8>::new(0).is_err());
        assert!(DynamicBufferP2::<u8>::new(3).is_err());
    }

    #[test]
    fn p2_buf() {
        for i in 0..25 {
            let size = 1 << i;
            assert!(DynamicBufferP2::<u8>::new(size).is_ok());
        }
    }

    fn test_at<T, B: Buffer<T>>(buf: &mut B) {
        let size = buf.size();
        for i in 0..size {
            assert_eq!(buf.at(i), buf.at(i));
            assert_eq!(buf.at_mut(i), buf.at_mut(i));
            assert_eq!(buf.at(i), buf.at(size + i));
            assert_eq!(buf.at_mut(i), buf.at_mut(size + i));
            assert!(buf.at(i) != buf.at(i + 1));
            assert!(buf.at_mut(i) != buf.at_mut(i + 1));
        }
    }

    #[test]
    fn dynamic_buf() {
        let mut buf = DynamicBuffer::<i32>::new(3).unwrap();
        assert_eq!(buf.size(), 3);
        test_at(&mut buf);
    }

    #[test]
    fn dynamic_buf_p2() {
        let mut buf = DynamicBufferP2::<i32>::new(4).unwrap();
        assert_eq!(buf.size(), 4);
        test_at(&mut buf);
    }
}