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

use std::cell::Cell;
use it_memory_traits::{SequentialReader, SequentialWriter};

#[macro_export]
macro_rules! value_der {
    ($self:expr, $offset:expr, @seq_start $($ids:tt),* @seq_end) => {
        [$($self.memory[$offset + $ids].get()),+]
    };

    ($self:expr, $offset:expr, 1) => {
        crate::value_der!($self, $offset, @seq_start 0 @seq_end);
    };

    ($self:expr, $offset:expr, 2) => {
        crate::value_der!($self, $offset, @seq_start 0, 1 @seq_end);
    };

    ($self:expr, $offset:expr, 4) => {
        crate::value_der!($self, $offset, @seq_start 0, 1, 2, 3 @seq_end);
    };

    ($self:expr, $offset:expr, 8) => {
        crate::value_der!($self, $offset, @seq_start 0, 1, 2, 3, 4, 5, 6, 7 @seq_end);
    };

    ($self:expr, $offset:expr, 16) => {
        crate::value_der!($self, $offset, @seq_start 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 @seq_end);
    };
}

#[macro_export]
macro_rules! read_ty {
    ($func_name:ident, $ty:ty, 1) => {
        fn $func_name(&self) -> $ty {
            let offset = self.offset.get();
            let result = <$ty>::from_le_bytes(crate::value_der!(self, offset, 1));

            self.offset.set(offset + 1);
            result
        }
    };

    ($func_name:ident, $ty:ty, 2) => {
        fn $func_name(&self) -> $ty {
            let offset = self.offset.get();
            let result = <$ty>::from_le_bytes(crate::value_der!(self, offset, 2));

            self.offset.set(offset + 2);
            result
        }
    };

    ($func_name:ident, $ty:ty, 4) => {
        fn $func_name(&self) -> $ty {
            let offset = self.offset.get();
            let result = <$ty>::from_le_bytes(crate::value_der!(self, offset, 4));

            self.offset.set(offset + 4);
            result
        }
    };

    ($func_name:ident, $ty:ty, 8) => {
        fn $func_name(&self) -> $ty {
            let offset = self.offset.get();
            let result = <$ty>::from_le_bytes(crate::value_der!(self, offset, 8));

            self.offset.set(offset + 8);
            result
        }
    };

    ($func_name:ident, $ty:ty, 16) => {
        fn $func_name(&self) -> $ty {
            let offset = self.offset.get();
            let result = <$ty>::from_le_bytes(crate::value_der!(self, offset, 16));

            self.offset.set(offset + 16);
            result
        }
    };
}

pub(crate) struct WasmerSequentialReader<'s> {
    pub memory: &'s [Cell<u8>],
    pub offset: Cell<u32>,
}

pub(crate) struct WasmerSequentialWriter<'s> {
    pub offset: u32,
    pub slice: &'s [Cell<u8>],
    pub current_offset: Cell<u32>,
}

impl SequentialReader for WasmerSequentialReader<'_> {
    fn read_byte(&self) -> u8 {
        let offset = self.offset.get();
        let result = self.memory[offset as usize].get();
        self.offset.set(offset + 1);
        result
    }

    // needed because clippy suggests using an iterator which looks worse
    #[allow(clippy::needless_range_loop)]
    fn read_bytes<const COUNT: usize>(&self) -> [u8; COUNT] {
        let offset = self.offset.get();
        let mut result = [0u8; COUNT];
        for index in 0..COUNT {
            result[index] = self.memory[offset as usize + index].get();
        }

        self.offset.set(offset + COUNT as u32);
        result
    }
}

impl SequentialWriter for WasmerSequentialWriter<'_> {
    fn start_offset(&self) -> u32 {
        self.offset
    }

    fn write_u8(&self, value: u8) {
        let offset = self.current_offset.get();
        self.slice[offset as usize].set(value);
        self.current_offset.set(offset + 1);
    }

    fn write_u32(&self, value: u32) {
        self.write_bytes(&value.to_le_bytes());
    }

    fn write_bytes(&self, bytes: &[u8]) {
        for byte in bytes {
            self.write_u8(*byte)
        }
    }
}