summaryrefslogtreecommitdiffstats
path: root/third_party/rust/scroll/src/leb128.rs
blob: eceec6d16613b3570986e9530d36a91e0bb4d59d (plain)
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
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
use core::convert::{AsRef, From};
use core::{result, u8};

use crate::ctx::TryFromCtx;
use crate::{error, Pread};

#[derive(Debug, PartialEq, Copy, Clone)]
/// An unsigned leb128 integer
pub struct Uleb128 {
    value: u64,
    count: usize,
}

impl Uleb128 {
    #[inline]
    /// Return how many bytes this Uleb128 takes up in memory
    pub fn size(&self) -> usize {
        self.count
    }
    #[inline]
    /// Read a variable length u64 from `bytes` at `offset`
    pub fn read(bytes: &[u8], offset: &mut usize) -> error::Result<u64> {
        let tmp = bytes.pread::<Uleb128>(*offset)?;
        *offset += tmp.size();
        Ok(tmp.into())
    }
}

impl AsRef<u64> for Uleb128 {
    fn as_ref(&self) -> &u64 {
        &self.value
    }
}

impl From<Uleb128> for u64 {
    #[inline]
    fn from(uleb128: Uleb128) -> u64 {
        uleb128.value
    }
}

#[derive(Debug, PartialEq, Copy, Clone)]
/// An signed leb128 integer
pub struct Sleb128 {
    value: i64,
    count: usize,
}

impl Sleb128 {
    #[inline]
    /// Return how many bytes this Sleb128 takes up in memory
    pub fn size(&self) -> usize {
        self.count
    }
    #[inline]
    /// Read a variable length i64 from `bytes` at `offset`
    pub fn read(bytes: &[u8], offset: &mut usize) -> error::Result<i64> {
        let tmp = bytes.pread::<Sleb128>(*offset)?;
        *offset += tmp.size();
        Ok(tmp.into())
    }
}

impl AsRef<i64> for Sleb128 {
    fn as_ref(&self) -> &i64 {
        &self.value
    }
}

impl From<Sleb128> for i64 {
    #[inline]
    fn from(sleb128: Sleb128) -> i64 {
        sleb128.value
    }
}

// Below implementation heavily adapted from: https://github.com/fitzgen/leb128
const CONTINUATION_BIT: u8 = 1 << 7;
const SIGN_BIT: u8 = 1 << 6;

#[inline]
fn mask_continuation(byte: u8) -> u8 {
    byte & !CONTINUATION_BIT
}

// #[inline]
// fn mask_continuation_u64(val: u64) -> u8 {
//     let byte = val & (u8::MAX as u64);
//     mask_continuation(byte as u8)
// }

impl<'a> TryFromCtx<'a> for Uleb128 {
    type Error = error::Error;
    #[inline]
    fn try_from_ctx(src: &'a [u8], _ctx: ()) -> result::Result<(Self, usize), Self::Error> {
        let mut result = 0;
        let mut shift = 0;
        let mut count = 0;
        loop {
            let byte: u8 = src.pread(count)?;

            if shift == 63 && byte != 0x00 && byte != 0x01 {
                return Err(error::Error::BadInput {
                    size: src.len(),
                    msg: "failed to parse",
                });
            }

            let low_bits = u64::from(mask_continuation(byte));
            result |= low_bits << shift;

            count += 1;
            shift += 7;

            if byte & CONTINUATION_BIT == 0 {
                return Ok((
                    Uleb128 {
                        value: result,
                        count,
                    },
                    count,
                ));
            }
        }
    }
}

impl<'a> TryFromCtx<'a> for Sleb128 {
    type Error = error::Error;
    #[inline]
    fn try_from_ctx(src: &'a [u8], _ctx: ()) -> result::Result<(Self, usize), Self::Error> {
        let o = 0;
        let offset = &mut 0;
        let mut result = 0;
        let mut shift = 0;
        let size = 64;
        let mut byte: u8;
        loop {
            byte = src.gread(offset)?;

            if shift == 63 && byte != 0x00 && byte != 0x7f {
                return Err(error::Error::BadInput {
                    size: src.len(),
                    msg: "failed to parse",
                });
            }

            let low_bits = i64::from(mask_continuation(byte));
            result |= low_bits << shift;
            shift += 7;

            if byte & CONTINUATION_BIT == 0 {
                break;
            }
        }

        if shift < size && (SIGN_BIT & byte) == SIGN_BIT {
            // Sign extend the result.
            result |= !0 << shift;
        }
        let count = *offset - o;
        Ok((
            Sleb128 {
                value: result,
                count,
            },
            count,
        ))
    }
}

#[cfg(test)]
mod tests {
    use super::super::LE;
    use super::{Sleb128, Uleb128};

    const CONTINUATION_BIT: u8 = 1 << 7;
    //const SIGN_BIT: u8 = 1 << 6;

    #[test]
    fn uleb_size() {
        use super::super::Pread;
        let buf = [2u8 | CONTINUATION_BIT, 1];
        let bytes = &buf[..];
        let num = bytes.pread::<Uleb128>(0).unwrap();
        #[cfg(feature = "std")]
        println!("num: {num:?}");
        assert_eq!(130u64, num.into());
        assert_eq!(num.size(), 2);

        let buf = [0x00, 0x01];
        let bytes = &buf[..];
        let num = bytes.pread::<Uleb128>(0).unwrap();
        #[cfg(feature = "std")]
        println!("num: {num:?}");
        assert_eq!(0u64, num.into());
        assert_eq!(num.size(), 1);

        let buf = [0x21];
        let bytes = &buf[..];
        let num = bytes.pread::<Uleb128>(0).unwrap();
        #[cfg(feature = "std")]
        println!("num: {num:?}");
        assert_eq!(0x21u64, num.into());
        assert_eq!(num.size(), 1);
    }

    #[test]
    fn uleb128() {
        use super::super::Pread;
        let buf = [2u8 | CONTINUATION_BIT, 1];
        let bytes = &buf[..];
        let num = bytes.pread::<Uleb128>(0).expect("Should read Uleb128");
        assert_eq!(130u64, num.into());
        assert_eq!(
            386,
            bytes.pread_with::<u16>(0, LE).expect("Should read number")
        );
    }

    #[test]
    fn uleb128_overflow() {
        use super::super::Pread;
        let buf = [
            2u8 | CONTINUATION_BIT,
            2 | CONTINUATION_BIT,
            2 | CONTINUATION_BIT,
            2 | CONTINUATION_BIT,
            2 | CONTINUATION_BIT,
            2 | CONTINUATION_BIT,
            2 | CONTINUATION_BIT,
            2 | CONTINUATION_BIT,
            2 | CONTINUATION_BIT,
            2 | CONTINUATION_BIT,
            1,
        ];
        let bytes = &buf[..];
        assert!(bytes.pread::<Uleb128>(0).is_err());
    }

    #[test]
    fn sleb128() {
        use super::super::Pread;
        let bytes = [0x7fu8 | CONTINUATION_BIT, 0x7e];
        let num: i64 = bytes
            .pread::<Sleb128>(0)
            .expect("Should read Sleb128")
            .into();
        assert_eq!(-129, num);
    }
}