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

//
// Copyright (c) 2016 KAMADA Ken'ichi.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions
// are met:
// 1. Redistributions of source code must retain the above copyright
//    notice, this list of conditions and the following disclaimer.
// 2. Redistributions in binary form must reproduce the above copyright
//    notice, this list of conditions and the following disclaimer in the
//    documentation and/or other materials provided with the distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
// OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
// HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
// LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
// OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
// SUCH DAMAGE.
//

use std::io;
use std::mem;

// This is a module to select endianess by using generics
// in order to avoid run-time dispatching penalty at the cost of
// increased object size.

pub trait Endian {
    fn loadu16(buf: &[u8], from: usize) -> u16;
    fn loadu32(buf: &[u8], from: usize) -> u32;
    fn loadu64(buf: &[u8], from: usize) -> u64;
    fn writeu16<W>(w: &mut W, num: u16) -> io::Result<()> where W: io::Write;
    fn writeu32<W>(w: &mut W, num: u32) -> io::Result<()> where W: io::Write;
    fn writeu64<W>(w: &mut W, num: u64) -> io::Result<()> where W: io::Write;
}

pub struct BigEndian;
pub struct LittleEndian;

macro_rules! generate_load {
    ($name:ident, $int_type:ident, $from_func:ident) => (
        fn $name(buf: &[u8], offset: usize) -> $int_type {
            let mut num = [0u8; mem::size_of::<$int_type>()];
            num.copy_from_slice(
                &buf[offset .. offset + mem::size_of::<$int_type>()]);
            $int_type::$from_func(num)
        }
    )
}

macro_rules! generate_write {
    ($name:ident, $int_type:ident, $to_func:ident) => (
        fn $name<W>(w: &mut W, num: $int_type)
                    -> io::Result<()> where W: io::Write {
            let buf = num.$to_func();
            w.write_all(&buf)
        }
    )
}

impl Endian for BigEndian {
    generate_load!(loadu16, u16, from_be_bytes);
    generate_load!(loadu32, u32, from_be_bytes);
    generate_load!(loadu64, u64, from_be_bytes);
    generate_write!(writeu16, u16, to_be_bytes);
    generate_write!(writeu32, u32, to_be_bytes);
    generate_write!(writeu64, u64, to_be_bytes);
}

impl Endian for LittleEndian {
    generate_load!(loadu16, u16, from_le_bytes);
    generate_load!(loadu32, u32, from_le_bytes);
    generate_load!(loadu64, u64, from_le_bytes);
    generate_write!(writeu16, u16, to_le_bytes);
    generate_write!(writeu32, u32, to_le_bytes);
    generate_write!(writeu64, u64, to_le_bytes);
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn loadu16() {
        assert_eq!(BigEndian::loadu16(&[0x01, 0x02], 0), 0x0102);
        assert_eq!(BigEndian::loadu16(&[0x01, 0x02, 0x03], 1), 0x0203);
        assert_eq!(LittleEndian::loadu16(&[0x01, 0x02], 0), 0x0201);
        assert_eq!(LittleEndian::loadu16(&[0x01, 0x02, 0x03], 1), 0x0302);
    }

    #[test]
    fn loadu32() {
        assert_eq!(BigEndian::loadu32(&[0x01, 0x02, 0x03, 0x04], 0),
                   0x01020304);
        assert_eq!(BigEndian::loadu32(&[0x01, 0x02, 0x03, 0x04, 0x05], 1),
                   0x02030405);
        assert_eq!(LittleEndian::loadu32(&[0x01, 0x02, 0x03, 0x04], 0),
                   0x04030201);
        assert_eq!(LittleEndian::loadu32(&[0x01, 0x02, 0x03, 0x04, 0x05], 1),
                   0x05040302);
    }

    #[test]
    fn loadu64() {
        assert_eq!(BigEndian::loadu64(&[0x01, 0x02, 0x03, 0x04,
                                        0x05, 0x06, 0x07, 0x08], 0),
                   0x0102030405060708);
        assert_eq!(BigEndian::loadu64(&[0x01, 0x02, 0x03, 0x04, 0x05,
                                        0x06, 0x07, 0x08, 0x09], 1),
                   0x0203040506070809);
        assert_eq!(LittleEndian::loadu64(&[0x01, 0x02, 0x03, 0x04,
                                           0x05, 0x06, 0x07, 0x08], 0),
                   0x0807060504030201);
        assert_eq!(LittleEndian::loadu64(&[0x01, 0x02, 0x03, 0x04, 0x05,
                                           0x06, 0x07, 0x08, 0x09], 1),
                   0x0908070605040302);
    }

    #[test]
    fn writeu16() {
        let mut buf = Vec::new();
        BigEndian::writeu16(&mut buf, 0x0102).unwrap();
        LittleEndian::writeu16(&mut buf, 0x0304).unwrap();
        assert_eq!(buf, b"\x01\x02\x04\x03");
    }

    #[test]
    fn writeu32() {
        let mut buf = Vec::new();
        BigEndian::writeu32(&mut buf, 0x01020304).unwrap();
        LittleEndian::writeu32(&mut buf, 0x05060708).unwrap();
        assert_eq!(buf, b"\x01\x02\x03\x04\x08\x07\x06\x05");
    }

    #[test]
    fn writeu64() {
        let mut buf = Vec::new();
        BigEndian::writeu64(&mut buf, 0x0102030405060708).unwrap();
        LittleEndian::writeu64(&mut buf, 0x090a0b0c0d0e0f10).unwrap();
        assert_eq!(buf, b"\x01\x02\x03\x04\x05\x06\x07\x08\
                          \x10\x0f\x0e\x0d\x0c\x0b\x0a\x09");
    }

    #[test]
    fn dispatch() {
        fn dispatch_sub<E>(data: &[u8]) -> u16 where E: Endian {
            E::loadu16(data, 0)
        }
        assert_eq!(dispatch_sub::<BigEndian>(&[0x01, 0x02]), 0x0102);
        assert_eq!(dispatch_sub::<LittleEndian>(&[0x01, 0x02]), 0x0201);
    }

    #[test]
    fn static_dispatch() {
        fn dispatch_sub<E>(data: &[u8]) -> u16 where E: Endian {
            E::loadu16(data, 0)
        }
        assert_eq!(dispatch_sub::<BigEndian> as *const (),
                   dispatch_sub::<BigEndian> as *const ());
        assert_ne!(dispatch_sub::<BigEndian> as *const (),
                   dispatch_sub::<LittleEndian> as *const ());
    }

    #[test]
    #[should_panic(expected = "index 3 out of range for slice of length 2")]
    fn out_of_range() {
        BigEndian::loadu16(&[0x01, 0x02], 1);
    }

    // "attempt to add with overflow" with the arithmetic overflow
    // check, and "slice index starts at 18446744073709551615 but ends
    // at 1" without it.
    #[test]
    #[should_panic(expected = "at")]
    fn wrap_around() {
        BigEndian::loadu16(&[0x01, 0x02], (-1isize) as usize);
    }
}