littlefs-rust-core 0.1.0

Port of LittleFS to unsafe rust
Documentation 
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

//! CRC-32. Per lfs_util.c lfs_crc.
//! Polynomial = 0x04c11db7, small lookup table.

const RTABLE: [u32; 16] = [
    0x0000_0000,
    0x1db7_1064,
    0x3b6e_20c8,
    0x26d9_30ac,
    0x76dc_4190,
    0x6b6b_51f4,
    0x4db2_6158,
    0x5005_713c,
    0xedb8_8320,
    0xf00f_9344,
    0xd6d6_a3e8,
    0xcb61_b38c,
    0x9b64_c2b0,
    0x86d3_d2d4,
    0xa00a_e278,
    0xbdbd_f21c,
];

/// Per lfs_util.c lfs_crc (lines 19-35)
///
/// C:
/// ```c
/// uint32_t lfs_crc(uint32_t crc, const void *buffer, size_t size) {
///     static const uint32_t rtable[16] = {
///         0x00000000, 0x1db71064, 0x3b6e20c8, 0x26d930ac,
///         0x76dc4190, 0x6b6b51f4, 0x4db26158, 0x5005713c,
///         0xedb88320, 0xf00f9344, 0xd6d6a3e8, 0xcb61b38c,
///         0x9b64c2b0, 0x86d3d2d4, 0xa00ae278, 0xbdbdf21c,
///     };
///     const uint8_t *data = buffer;
///     for (size_t i = 0; i < size; i++) {
///         crc = (crc >> 4) ^ rtable[(crc ^ (data[i] >> 0)) & 0xf];
///         crc = (crc >> 4) ^ rtable[(crc ^ (data[i] >> 4)) & 0xf];
///     }
///     return crc;
/// }
/// ```
#[inline(always)]
pub fn lfs_crc(crc: u32, buffer: *const u8, size: usize) -> u32 {
    let mut crc = crc;
    let data = buffer;
    unsafe {
        for i in 0..size {
            let byte = *data.add(i);
            let idx = ((crc ^ byte as u32) & 0xf) as usize;
            crc = (crc >> 4) ^ RTABLE[idx];
            let idx = ((crc ^ (byte >> 4) as u32) & 0xf) as usize;
            crc = (crc >> 4) ^ RTABLE[idx];
        }
    }
    crc
}