diff options
author | Joe Crayne <joe@jerkface.net> | 2019-11-29 22:33:01 -0500 |
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committer | Joe Crayne <joe@jerkface.net> | 2020-01-01 23:22:43 -0500 |
commit | 2f823f082afc9f7501f2672435ca764e964a3bae (patch) | |
tree | faaabf62a726c9305c12ff132eb4b9f556dd9dd4 /dht/cbits | |
parent | fddb44cc648da0494be580b832a0b5a61b27f2ff (diff) |
Switched z-base32 to use 4-bit crc.
Diffstat (limited to 'dht/cbits')
-rw-r--r-- | dht/cbits/crc4_itu.c | 44 |
1 files changed, 44 insertions, 0 deletions
diff --git a/dht/cbits/crc4_itu.c b/dht/cbits/crc4_itu.c new file mode 100644 index 00000000..8e3b0489 --- /dev/null +++ b/dht/cbits/crc4_itu.c | |||
@@ -0,0 +1,44 @@ | |||
1 | /*----------------------------------------------------------------- | ||
2 | | crc4_itu.c | ||
3 | | | ||
4 | | CRC4-ITU library using lookup table method. | ||
5 | | | ||
6 | *-------------------------------------------------------------------*/ | ||
7 | |||
8 | #include <stddef.h> | ||
9 | |||
10 | static unsigned char const crc4itu_bbox[256] = { | ||
11 | 0x0, 0x7, 0xe, 0x9, 0x5, 0x2, 0xb, 0xc, 0xa, 0xd, 0x4, 0x3, 0xf, 0x8, 0x1, 0x6, | ||
12 | 0xd, 0xa, 0x3, 0x4, 0x8, 0xf, 0x6, 0x1, 0x7, 0x0, 0x9, 0xe, 0x2, 0x5, 0xc, 0xb, | ||
13 | 0x3, 0x4, 0xd, 0xa, 0x6, 0x1, 0x8, 0xf, 0x9, 0xe, 0x7, 0x0, 0xc, 0xb, 0x2, 0x5, | ||
14 | 0xe, 0x9, 0x0, 0x7, 0xb, 0xc, 0x5, 0x2, 0x4, 0x3, 0xa, 0xd, 0x1, 0x6, 0xf, 0x8, | ||
15 | 0x6, 0x1, 0x8, 0xf, 0x3, 0x4, 0xd, 0xa, 0xc, 0xb, 0x2, 0x5, 0x9, 0xe, 0x7, 0x0, | ||
16 | 0xb, 0xc, 0x5, 0x2, 0xe, 0x9, 0x0, 0x7, 0x1, 0x6, 0xf, 0x8, 0x4, 0x3, 0xa, 0xd, | ||
17 | 0x5, 0x2, 0xb, 0xc, 0x0, 0x7, 0xe, 0x9, 0xf, 0x8, 0x1, 0x6, 0xa, 0xd, 0x4, 0x3, | ||
18 | 0x8, 0xf, 0x6, 0x1, 0xd, 0xa, 0x3, 0x4, 0x2, 0x5, 0xc, 0xb, 0x7, 0x0, 0x9, 0xe, | ||
19 | 0xc, 0xb, 0x2, 0x5, 0x9, 0xe, 0x7, 0x0, 0x6, 0x1, 0x8, 0xf, 0x3, 0x4, 0xd, 0xa, | ||
20 | 0x1, 0x6, 0xf, 0x8, 0x4, 0x3, 0xa, 0xd, 0xb, 0xc, 0x5, 0x2, 0xe, 0x9, 0x0, 0x7, | ||
21 | 0xf, 0x8, 0x1, 0x6, 0xa, 0xd, 0x4, 0x3, 0x5, 0x2, 0xb, 0xc, 0x0, 0x7, 0xe, 0x9, | ||
22 | 0x2, 0x5, 0xc, 0xb, 0x7, 0x0, 0x9, 0xe, 0x8, 0xf, 0x6, 0x1, 0xd, 0xa, 0x3, 0x4, | ||
23 | 0xa, 0xd, 0x4, 0x3, 0xf, 0x8, 0x1, 0x6, 0x0, 0x7, 0xe, 0x9, 0x5, 0x2, 0xb, 0xc, | ||
24 | 0x7, 0x0, 0x9, 0xe, 0x2, 0x5, 0xc, 0xb, 0xd, 0xa, 0x3, 0x4, 0x8, 0xf, 0x6, 0x1, | ||
25 | 0x9, 0xe, 0x7, 0x0, 0xc, 0xb, 0x2, 0x5, 0x3, 0x4, 0xd, 0xa, 0x6, 0x1, 0x8, 0xf, | ||
26 | 0x4, 0x3, 0xa, 0xd, 0x1, 0x6, 0xf, 0x8, 0xe, 0x9, 0x0, 0x7, 0xb, 0xc, 0x5, 0x2 | ||
27 | }; | ||
28 | |||
29 | /** | ||
30 | * CRC4-ITU function | ||
31 | * | ||
32 | * Parameters: | ||
33 | * crc Existing CRC value (usually 0x00) before process a new one. | ||
34 | * data Pointer to data to be hashed with CRC | ||
35 | * len Size of data | ||
36 | * | ||
37 | * Returns: CRC value in lowest 4 bits. | ||
38 | */ | ||
39 | unsigned char crc4itu(unsigned char crc, unsigned char *data, unsigned int len) { | ||
40 | if (data == NULL) return 0; | ||
41 | crc &= 0xf; | ||
42 | while (len--) crc = crc4itu_bbox[crc ^ *data++]; | ||
43 | return crc; | ||
44 | } | ||