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1 | // Copyright 2012-2015 The Rust Project Developers. See the COPYRIGHT |
2 | // file at the top-level directory of this distribution and at | |
3 | // http://rust-lang.org/COPYRIGHT. | |
4 | // | |
5 | // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or | |
6 | // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license | |
7 | // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your | |
8 | // option. This file may not be copied, modified, or distributed | |
9 | // except according to those terms. | |
10 | ||
11 | #[inline] | |
12 | pub fn write_to_vec(vec: &mut Vec<u8>, position: &mut usize, byte: u8) { | |
13 | if *position == vec.len() { | |
14 | vec.push(byte); | |
15 | } else { | |
16 | vec[*position] = byte; | |
17 | } | |
18 | ||
19 | *position += 1; | |
20 | } | |
21 | ||
22 | pub fn write_unsigned_leb128(out: &mut Vec<u8>, start_position: usize, mut value: u64) -> usize { | |
23 | let mut position = start_position; | |
24 | loop { | |
25 | let mut byte = (value & 0x7F) as u8; | |
26 | value >>= 7; | |
27 | if value != 0 { | |
28 | byte |= 0x80; | |
29 | } | |
30 | ||
31 | write_to_vec(out, &mut position, byte); | |
32 | ||
33 | if value == 0 { | |
34 | break; | |
35 | } | |
36 | } | |
37 | ||
38 | return position - start_position; | |
39 | } | |
40 | ||
41 | pub fn read_unsigned_leb128(data: &[u8], start_position: usize) -> (u64, usize) { | |
42 | let mut result = 0; | |
43 | let mut shift = 0; | |
44 | let mut position = start_position; | |
45 | loop { | |
46 | let byte = data[position]; | |
47 | position += 1; | |
48 | result |= ((byte & 0x7F) as u64) << shift; | |
49 | if (byte & 0x80) == 0 { | |
50 | break; | |
51 | } | |
52 | shift += 7; | |
53 | } | |
54 | ||
55 | (result, position - start_position) | |
56 | } | |
57 | ||
58 | ||
59 | pub fn write_signed_leb128(out: &mut Vec<u8>, start_position: usize, mut value: i64) -> usize { | |
60 | let mut position = start_position; | |
61 | ||
62 | loop { | |
63 | let mut byte = (value as u8) & 0x7f; | |
64 | value >>= 7; | |
65 | let more = !((((value == 0) && ((byte & 0x40) == 0)) || | |
66 | ((value == -1) && ((byte & 0x40) != 0)))); | |
67 | if more { | |
68 | byte |= 0x80; // Mark this byte to show that more bytes will follow. | |
69 | } | |
70 | ||
71 | write_to_vec(out, &mut position, byte); | |
72 | ||
73 | if !more { | |
74 | break; | |
75 | } | |
76 | } | |
77 | ||
78 | return position - start_position; | |
79 | } | |
80 | ||
81 | pub fn read_signed_leb128(data: &[u8], start_position: usize) -> (i64, usize) { | |
82 | let mut result = 0; | |
83 | let mut shift = 0; | |
84 | let mut position = start_position; | |
85 | let mut byte; | |
86 | ||
87 | loop { | |
88 | byte = data[position]; | |
89 | position += 1; | |
90 | result |= ((byte & 0x7F) as i64) << shift; | |
91 | shift += 7; | |
92 | ||
93 | if (byte & 0x80) == 0 { | |
94 | break; | |
95 | } | |
96 | } | |
97 | ||
98 | if (shift < 64) && ((byte & 0x40) != 0) { | |
99 | // sign extend | |
100 | result |= -(1i64 << shift); | |
101 | } | |
102 | ||
103 | (result, position - start_position) | |
104 | } | |
105 | ||
106 | #[test] | |
107 | fn test_unsigned_leb128() { | |
108 | let mut stream = Vec::with_capacity(10000); | |
109 | ||
110 | for x in 0..62 { | |
111 | let pos = stream.len(); | |
112 | let bytes_written = write_unsigned_leb128(&mut stream, pos, 3 << x); | |
113 | assert_eq!(stream.len(), pos + bytes_written); | |
114 | } | |
115 | ||
116 | let mut position = 0; | |
117 | for x in 0..62 { | |
118 | let expected = 3 << x; | |
119 | let (actual, bytes_read) = read_unsigned_leb128(&stream, position); | |
120 | assert_eq!(expected, actual); | |
121 | position += bytes_read; | |
122 | } | |
123 | assert_eq!(stream.len(), position); | |
124 | } | |
125 | ||
126 | #[test] | |
127 | fn test_signed_leb128() { | |
128 | let mut values = Vec::new(); | |
129 | ||
130 | let mut i = -500; | |
131 | while i < 500 { | |
132 | values.push(i * 123457i64); | |
133 | i += 1; | |
134 | } | |
135 | ||
136 | let mut stream = Vec::new(); | |
137 | ||
138 | for &x in &values { | |
139 | let pos = stream.len(); | |
140 | let bytes_written = write_signed_leb128(&mut stream, pos, x); | |
141 | assert_eq!(stream.len(), pos + bytes_written); | |
142 | } | |
143 | ||
144 | let mut pos = 0; | |
145 | for &x in &values { | |
146 | let (value, bytes_read) = read_signed_leb128(&mut stream, pos); | |
147 | pos += bytes_read; | |
148 | assert_eq!(x, value); | |
149 | } | |
150 | assert_eq!(pos, stream.len()); | |
151 | } |