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
|
macro_rules! impl_write_unsigned_leb128 {
($fn_name:ident, $int_ty:ident) => {
#[inline]
pub fn $fn_name(out: &mut Vec<u8>, mut value: $int_ty) {
loop {
if value < 0x80 {
out.push(value as u8);
break;
} else {
out.push(((value & 0x7f) | 0x80) as u8);
value >>= 7;
}
}
}
};
}
impl_write_unsigned_leb128!(write_u16_leb128, u16);
impl_write_unsigned_leb128!(write_u32_leb128, u32);
impl_write_unsigned_leb128!(write_u64_leb128, u64);
impl_write_unsigned_leb128!(write_u128_leb128, u128);
impl_write_unsigned_leb128!(write_usize_leb128, usize);
macro_rules! impl_read_unsigned_leb128 {
($fn_name:ident, $int_ty:ident) => {
#[inline]
pub fn $fn_name(slice: &[u8]) -> ($int_ty, usize) {
let mut result = 0;
let mut shift = 0;
let mut position = 0;
loop {
let byte = slice[position];
position += 1;
if (byte & 0x80) == 0 {
result |= (byte as $int_ty) << shift;
return (result, position);
} else {
result |= ((byte & 0x7F) as $int_ty) << shift;
}
shift += 7;
}
}
};
}
impl_read_unsigned_leb128!(read_u16_leb128, u16);
impl_read_unsigned_leb128!(read_u32_leb128, u32);
impl_read_unsigned_leb128!(read_u64_leb128, u64);
impl_read_unsigned_leb128!(read_u128_leb128, u128);
impl_read_unsigned_leb128!(read_usize_leb128, usize);
#[inline]
/// encodes an integer using signed leb128 encoding and stores
/// the result using a callback function.
///
/// The callback `write` is called once for each position
/// that is to be written to with the byte to be encoded
/// at that position.
pub fn write_signed_leb128_to<W>(mut value: i128, mut write: W)
where
W: FnMut(u8),
{
loop {
let mut byte = (value as u8) & 0x7f;
value >>= 7;
let more =
!(((value == 0) && ((byte & 0x40) == 0)) || ((value == -1) && ((byte & 0x40) != 0)));
if more {
byte |= 0x80; // Mark this byte to show that more bytes will follow.
}
write(byte);
if !more {
break;
}
}
}
#[inline]
pub fn write_signed_leb128(out: &mut Vec<u8>, value: i128) {
write_signed_leb128_to(value, |v| out.push(v))
}
#[inline]
pub fn read_signed_leb128(data: &[u8], start_position: usize) -> (i128, usize) {
let mut result = 0;
let mut shift = 0;
let mut position = start_position;
let mut byte;
loop {
byte = data[position];
position += 1;
result |= i128::from(byte & 0x7F) << shift;
shift += 7;
if (byte & 0x80) == 0 {
break;
}
}
if (shift < 64) && ((byte & 0x40) != 0) {
// sign extend
result |= -(1 << shift);
}
(result, position - start_position)
}
|
