crc/
crc32.rs

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1use crate::util::crc32;
2use crc_catalog::Algorithm;
3
4mod bytewise;
5mod nolookup;
6mod slice16;
7
8// init is shared between all impls
9const fn init(algorithm: &Algorithm<u32>, initial: u32) -> u32 {
10    if algorithm.refin {
11        initial.reverse_bits() >> (32u8 - algorithm.width)
12    } else {
13        initial << (32u8 - algorithm.width)
14    }
15}
16
17// finalize is shared between all impls
18const fn finalize(algorithm: &Algorithm<u32>, mut crc: u32) -> u32 {
19    if algorithm.refin ^ algorithm.refout {
20        crc = crc.reverse_bits();
21    }
22    if !algorithm.refout {
23        crc >>= 32u8 - algorithm.width;
24    }
25    crc ^ algorithm.xorout
26}
27
28const fn update_nolookup(mut crc: u32, algorithm: &Algorithm<u32>, bytes: &[u8]) -> u32 {
29    let poly = if algorithm.refin {
30        let poly = algorithm.poly.reverse_bits();
31        poly >> (32u8 - algorithm.width)
32    } else {
33        algorithm.poly << (32u8 - algorithm.width)
34    };
35
36    let mut i = 0;
37    if algorithm.refin {
38        while i < bytes.len() {
39            let to_crc = (crc ^ bytes[i] as u32) & 0xFF;
40            crc = crc32(poly, algorithm.refin, to_crc) ^ (crc >> 8);
41            i += 1;
42        }
43    } else {
44        while i < bytes.len() {
45            let to_crc = ((crc >> 24) ^ bytes[i] as u32) & 0xFF;
46            crc = crc32(poly, algorithm.refin, to_crc) ^ (crc << 8);
47            i += 1;
48        }
49    }
50    crc
51}
52
53const fn update_bytewise(mut crc: u32, reflect: bool, table: &[u32; 256], bytes: &[u8]) -> u32 {
54    let mut i = 0;
55    if reflect {
56        while i < bytes.len() {
57            let table_index = ((crc ^ bytes[i] as u32) & 0xFF) as usize;
58            crc = table[table_index] ^ (crc >> 8);
59            i += 1;
60        }
61    } else {
62        while i < bytes.len() {
63            let table_index = (((crc >> 24) ^ bytes[i] as u32) & 0xFF) as usize;
64            crc = table[table_index] ^ (crc << 8);
65            i += 1;
66        }
67    }
68    crc
69}
70
71const fn update_slice16(
72    mut crc: u32,
73    reflect: bool,
74    table: &[[u32; 256]; 16],
75    bytes: &[u8],
76) -> u32 {
77    let mut i = 0;
78    if reflect {
79        while i + 16 <= bytes.len() {
80            let mut current_slice = [bytes[i], bytes[i + 1], bytes[i + 2], bytes[i + 3]];
81
82            current_slice[0] ^= crc as u8;
83            current_slice[1] ^= (crc >> 8) as u8;
84            current_slice[2] ^= (crc >> 16) as u8;
85            current_slice[3] ^= (crc >> 24) as u8;
86
87            crc = table[0][bytes[i + 15] as usize]
88                ^ table[1][bytes[i + 14] as usize]
89                ^ table[2][bytes[i + 13] as usize]
90                ^ table[3][bytes[i + 12] as usize]
91                ^ table[4][bytes[i + 11] as usize]
92                ^ table[5][bytes[i + 10] as usize]
93                ^ table[6][bytes[i + 9] as usize]
94                ^ table[7][bytes[i + 8] as usize]
95                ^ table[8][bytes[i + 7] as usize]
96                ^ table[9][bytes[i + 6] as usize]
97                ^ table[10][bytes[i + 5] as usize]
98                ^ table[11][bytes[i + 4] as usize]
99                ^ table[12][current_slice[3] as usize]
100                ^ table[13][current_slice[2] as usize]
101                ^ table[14][current_slice[1] as usize]
102                ^ table[15][current_slice[0] as usize];
103
104            i += 16;
105        }
106
107        // Last few bytes
108        while i < bytes.len() {
109            let table_index = ((crc ^ bytes[i] as u32) & 0xFF) as usize;
110            crc = table[0][table_index] ^ (crc >> 8);
111            i += 1;
112        }
113    } else {
114        while i + 16 <= bytes.len() {
115            let mut current_slice = [bytes[i], bytes[i + 1], bytes[i + 2], bytes[i + 3]];
116
117            current_slice[0] ^= (crc >> 24) as u8;
118            current_slice[1] ^= (crc >> 16) as u8;
119            current_slice[2] ^= (crc >> 8) as u8;
120            current_slice[3] ^= crc as u8;
121
122            crc = table[0][bytes[i + 15] as usize]
123                ^ table[1][bytes[i + 14] as usize]
124                ^ table[2][bytes[i + 13] as usize]
125                ^ table[3][bytes[i + 12] as usize]
126                ^ table[4][bytes[i + 11] as usize]
127                ^ table[5][bytes[i + 10] as usize]
128                ^ table[6][bytes[i + 9] as usize]
129                ^ table[7][bytes[i + 8] as usize]
130                ^ table[8][bytes[i + 7] as usize]
131                ^ table[9][bytes[i + 6] as usize]
132                ^ table[10][bytes[i + 5] as usize]
133                ^ table[11][bytes[i + 4] as usize]
134                ^ table[12][current_slice[3] as usize]
135                ^ table[13][current_slice[2] as usize]
136                ^ table[14][current_slice[1] as usize]
137                ^ table[15][current_slice[0] as usize];
138
139            i += 16;
140        }
141
142        // Last few bytes
143        while i < bytes.len() {
144            let table_index = (((crc >> 24) ^ bytes[i] as u32) & 0xFF) as usize;
145            crc = table[0][table_index] ^ (crc << 8);
146            i += 1;
147        }
148    }
149    crc
150}
151
152#[cfg(test)]
153mod test {
154    use crate::*;
155    use crc_catalog::{Algorithm, CRC_32_ISCSI};
156
157    /// Test this optimized version against the well known implementation to ensure correctness
158    #[test]
159    fn correctness() {
160        let data: &[&str] = &[
161        "",
162        "1",
163        "1234",
164        "123456789",
165        "0123456789ABCDE",
166        "01234567890ABCDEFGHIJK",
167        "01234567890ABCDEFGHIJK01234567890ABCDEFGHIJK01234567890ABCDEFGHIJK01234567890ABCDEFGHIJK01234567890ABCDEFGHIJK01234567890ABCDEFGHIJK01234567890ABCDEFGHIJK01234567890ABCDEFGHIJK01234567890ABCDEFGHIJK01234567890ABCDEFGHIJK01234567890ABCDEFGHIJK01234567890ABCDEFGHIJK",
168    ];
169
170        pub const CRC_32_ISCSI_NONREFLEX: Algorithm<u32> = Algorithm {
171            width: 32,
172            poly: 0x1edc6f41,
173            init: 0xffffffff,
174            // This is the only flag that affects the optimized code path
175            refin: false,
176            refout: true,
177            xorout: 0xffffffff,
178            check: 0xe3069283,
179            residue: 0xb798b438,
180        };
181
182        let algs_to_test = [&CRC_32_ISCSI, &CRC_32_ISCSI_NONREFLEX];
183
184        for alg in algs_to_test {
185            for data in data {
186                let crc_slice16 = Crc::<u32, Table<16>>::new(alg);
187                let crc_nolookup = Crc::<u32, NoTable>::new(alg);
188                let expected = Crc::<u32, Table<1>>::new(alg).checksum(data.as_bytes());
189
190                // Check that doing all at once works as expected
191                assert_eq!(crc_slice16.checksum(data.as_bytes()), expected);
192                assert_eq!(crc_nolookup.checksum(data.as_bytes()), expected);
193
194                let mut digest = crc_slice16.digest();
195                digest.update(data.as_bytes());
196                assert_eq!(digest.finalize(), expected);
197
198                let mut digest = crc_nolookup.digest();
199                digest.update(data.as_bytes());
200                assert_eq!(digest.finalize(), expected);
201
202                // Check that we didn't break updating from multiple sources
203                if data.len() > 2 {
204                    let data = data.as_bytes();
205                    let data1 = &data[..data.len() / 2];
206                    let data2 = &data[data.len() / 2..];
207                    let mut digest = crc_slice16.digest();
208                    digest.update(data1);
209                    digest.update(data2);
210                    assert_eq!(digest.finalize(), expected);
211                    let mut digest = crc_nolookup.digest();
212                    digest.update(data1);
213                    digest.update(data2);
214                    assert_eq!(digest.finalize(), expected);
215                }
216            }
217        }
218    }
219}
crc/crc32.rs

crc/
crc32.rs
