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comparison crc32-table.c @ 0:422835bc1aca

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*: checkin
author Paper <paper@tflc.us>
date Mon, 09 Feb 2026 01:15:00 -0500
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-1:000000000000 0:422835bc1aca
1 #include "crc32i.h"
2
3 /* This builds our CRC table at compile-time rather than runtime.
4 * Note: We should have a way to change the polynomial at runtime too. */
5
6 #define CRC32_MASK(crc) (-((crc) & 1))
7
8 /* Does one iteration of the 8-time loop to generate one byte of the CRC table. */
9 #define CRC32_PRECALC_EX(crc) (((crc) >> 1) ^ ((CRC32_POLYNOMIAL) & CRC32_MASK(crc)))
10
11 /* Does all eight iterations of the loop to generate one byte. */
12 #define CRC32_PRECALC_E(byte) \
13 (CRC32_PRECALC_EX(CRC32_PRECALC_EX(CRC32_PRECALC_EX(CRC32_PRECALC_EX(CRC32_PRECALC_EX(CRC32_PRECALC_EX(CRC32_PRECALC_EX(CRC32_PRECALC_EX(byte)))))))))
14
15 /* Simple wrapper of CRC32_PRECALC_E that converts everything to uint32_t */
16 #define CRC32_PRECALC(byte) \
17 CRC32_PRECALC_E((uint32_t)(byte))
18
19 #define CRC32_PRECALC_0(byte) \
20 CRC32_PRECALC(byte), CRC32_PRECALC((byte) | 0x01)
21
22 #define CRC32_PRECALC_1(byte) \
23 CRC32_PRECALC_0(byte), CRC32_PRECALC_0((byte) | UINT32_C(0x02))
24
25 #define CRC32_PRECALC_2(byte) \
26 CRC32_PRECALC_1(byte), CRC32_PRECALC_1((byte) | UINT32_C(0x04))
27
28 #define CRC32_PRECALC_3(byte) \
29 CRC32_PRECALC_2(byte), CRC32_PRECALC_2((byte) | UINT32_C(0x08))
30
31 #define CRC32_PRECALC_4(byte) \
32 CRC32_PRECALC_3(byte), CRC32_PRECALC_3((byte) | UINT32_C(0x10))
33
34 #define CRC32_PRECALC_5(byte) \
35 CRC32_PRECALC_4(byte), CRC32_PRECALC_4((byte) | UINT32_C(0x20))
36
37 #define CRC32_PRECALC_6(byte) \
38 CRC32_PRECALC_5(byte), CRC32_PRECALC_5((byte) | UINT32_C(0x40))
39
40 #define CRC32_PRECALC_7(byte) \
41 CRC32_PRECALC_6(byte), CRC32_PRECALC_6((byte) | UINT32_C(0x80))
42
43 const uint32_t crc32_tab[256] = {
44 CRC32_PRECALC_7(0)
45 };
46
47 #undef CRC32_MASK
48 #undef CRC32_PRECALC_EX
49 #undef CRC32_PRECALC_E
50 #undef CRC32_PRECALC
51 #undef CRC32_PRECALC_0
52 #undef CRC32_PRECALC_1
53 #undef CRC32_PRECALC_2
54 #undef CRC32_PRECALC_3
55 #undef CRC32_PRECALC_4
56 #undef CRC32_PRECALC_5
57 #undef CRC32_PRECALC_6
58 #undef CRC32_PRECALC_7