ppmd-rust 1.4.1

PPMd compression / decompression
Documentation 
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
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166

use std::ptr::NonNull;

#[cfg(feature = "unstable-tagged-offsets")]
const TAG_MASK: u32 = 0xE0000000;
#[cfg(feature = "unstable-tagged-offsets")]
const OFFSET_MASK: u32 = 0x1FFFFFFF;
const TAG_NULL: u32 = 0;
#[allow(dead_code)]
pub(crate) const TAG_BYTES: u32 = 1 << 29;
#[allow(dead_code)]
pub(crate) const TAG_NODE: u32 = 2 << 29;
#[allow(dead_code)]
pub(crate) const TAG_STATE: u32 = 3 << 29;
#[allow(dead_code)]
pub(crate) const TAG_CONTEXT: u32 = 4 << 29;

#[allow(dead_code)]
pub(crate) trait Pointee {
    const TAG: u32;
}

impl Pointee for u8 {
    const TAG: u32 = TAG_BYTES;
}

pub(crate) trait MemoryAllocator {
    fn base_memory_ptr(&self) -> NonNull<u8>;
    #[cfg(not(feature = "unstable-tagged-offsets"))]
    fn units_start(&self) -> NonNull<u8>;
    #[cfg(feature = "unstable-tagged-offsets")]
    fn size(&self) -> u32;
}

#[derive(Copy, Clone, Debug, PartialEq, Eq, Default)]
#[repr(transparent)]
pub(crate) struct TaggedOffset(u32);

#[cfg(feature = "unstable-tagged-offsets")]
impl TaggedOffset {
    pub(crate) const fn null() -> TaggedOffset {
        TaggedOffset(TAG_NULL)
    }

    #[inline(always)]
    pub(crate) const fn from_raw(raw: u32) -> Self {
        Self(raw)
    }

    #[inline(always)]
    pub(crate) const fn from_bytes_offset(raw: u32) -> Self {
        TaggedOffset::from_raw((raw & OFFSET_MASK) | TAG_BYTES)
    }

    #[inline(always)]
    pub(crate) unsafe fn from_ptr<T: Pointee, A: MemoryAllocator>(
        allocator: &A,
        ptr: NonNull<T>,
    ) -> TaggedOffset {
        let offset = ptr.cast().offset_from(allocator.base_memory_ptr());
        let offset = u32::try_from(offset).expect("Failed to convert ptr to offset");
        let val = (offset & OFFSET_MASK) | T::TAG;
        Self(val)
    }

    #[inline(always)]
    pub(crate) fn is_null(&self) -> bool {
        self.0 == TAG_NULL
    }

    #[inline(always)]
    pub(crate) fn is_not_null(&self) -> bool {
        self.0 != TAG_NULL
    }

    #[inline(always)]
    pub(crate) fn get_offset(&self) -> u32 {
        self.0 & OFFSET_MASK
    }

    #[inline(always)]
    pub(crate) fn as_raw(&self) -> u32 {
        self.0
    }

    #[inline(always)]
    pub(crate) unsafe fn as_ptr<T: Pointee, A: MemoryAllocator>(
        &self,
        allocator: &A,
    ) -> NonNull<T> {
        let offset = self.get_offset();

        assert_eq!(self.0 & TAG_MASK, T::TAG, "Mismatched pointer type tag");
        assert!(offset < allocator.size(), "Out of bound access");

        allocator.base_memory_ptr().offset(offset as isize).cast()
    }

    pub(crate) fn is_real_context<A: MemoryAllocator>(&self, _allocator: &A) -> bool {
        (self.0 & TAG_MASK) == TAG_CONTEXT
    }
}

#[cfg(not(feature = "unstable-tagged-offsets"))]
impl TaggedOffset {
    pub(crate) const fn null() -> TaggedOffset {
        TaggedOffset(TAG_NULL)
    }

    #[inline(always)]
    pub(crate) const fn from_raw(raw: u32) -> Self {
        Self(raw)
    }

    #[inline(always)]
    pub(crate) const fn from_bytes_offset(raw: u32) -> Self {
        TaggedOffset::from_raw(raw)
    }

    #[inline(always)]
    pub(crate) unsafe fn from_ptr<T: Pointee, A: MemoryAllocator>(
        allocator: &A,
        ptr: NonNull<T>,
    ) -> TaggedOffset {
        let offset = ptr.cast().offset_from(allocator.base_memory_ptr());
        let offset = u32::try_from(offset).expect("Failed to convert ptr to offset");
        Self(offset)
    }

    #[inline(always)]
    pub(crate) fn is_null(&self) -> bool {
        self.0 == TAG_NULL
    }

    #[inline(always)]
    pub(crate) fn is_not_null(&self) -> bool {
        self.0 != TAG_NULL
    }

    #[inline(always)]
    pub(crate) fn get_offset(&self) -> u32 {
        self.0
    }

    #[inline(always)]
    pub(crate) fn as_raw(&self) -> u32 {
        self.0
    }

    #[inline(always)]
    pub(crate) unsafe fn as_ptr<T: Pointee, A: MemoryAllocator>(
        &self,
        allocator: &A,
    ) -> NonNull<T> {
        let offset = self.get_offset();
        allocator.base_memory_ptr().offset(offset as isize).cast()
    }

    pub(crate) unsafe fn is_real_context<A: MemoryAllocator>(&self, allocator: &A) -> bool {
        // A "real" context must be in the unit area and not in the text buffer area.
        let ptr = allocator
            .base_memory_ptr()
            .offset(self.get_offset() as isize)
            .cast();
        ptr >= allocator.units_start()
    }
}