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ssfcrc32 — 32-bit CCITT-32 CRC

SSF | EDC

32-bit CRC using the 0x04C11DB7 polynomial, compatible with CCITT-32 and ISO 3309.

The computation uses a 1024-byte lookup table for speed. A single call covers a contiguous buffer; successive calls with the previous return value as crc accumulate across non-contiguous or streaming chunks and produce the same result as one call over the whole dataset.

Dependencies | Notes | Configuration | API Summary | Function Reference

↑ Dependencies

↑ Notes

  • Always pass SSF_CRC32_INITIAL as crc for the first call in a sequence; pass the return value of the previous call for each subsequent chunk.
  • Requires 1024 bytes of program memory for the lookup table.
  • Compatible with CCITT-32 and ISO 3309 (polynomial 0x04C11DB7, initial value 0x00000000).
  • Strongly recommended alongside Reed-Solomon ECC: Reed-Solomon can correct to the wrong message without detecting the error; a CRC-32 check catches this false positive.
  • For lighter error detection with a smaller table see ssfcrc16.

↑ Configuration

This module has no compile-time configuration options in ssfoptions.h.

↑ API Summary

Definitions

Symbol Kind Description
SSF_CRC32_INITIAL Constant 0 — initial CRC state; pass as crc to begin a fresh computation

Functions

Function Description
e.g. uint32_t SSFCRC32(in, inLen, crc) Compute or accumulate a 32-bit CRC over a byte buffer

↑ Function Reference

↑ uint32_t SSFCRC32()

uint32_t SSFCRC32(const uint8_t *in, uint32_t inLen, uint32_t crc);

Computes or accumulates a 32-bit CCITT-32 CRC (polynomial 0x04C11DB7) over inLen bytes starting at in. May be called repeatedly on successive chunks; passing the return value of one call as crc to the next produces the same result as a single call over all chunks concatenated.

Parameter Direction Type Description
in in const uint8_t * Pointer to the input bytes. Must not be NULL when inLen > 0.
inLen in uint32_t Number of bytes to process.
crc in uint32_t Starting CRC state. Pass SSF_CRC32_INITIAL to begin a new computation; pass the return value of the previous call to continue an incremental computation.

Returns: Updated 32-bit CRC state. Pass this value as crc to the next call when processing data in multiple chunks, or compare it against an expected CRC for verification.

Example:

uint32_t crc;

/* Single-buffer computation */
crc = SSFCRC32((uint8_t *)"abcde", 5, SSF_CRC32_INITIAL);
/* crc == 0x8587D865 */

/* Incremental computation over chunks — same result */
crc = SSFCRC32((uint8_t *)"a",   1, SSF_CRC32_INITIAL);
crc = SSFCRC32((uint8_t *)"bcd", 3, crc);
crc = SSFCRC32((uint8_t *)"e",   1, crc);
/* crc == 0x8587D865 */

/* Verifying received data against a known CRC */
uint8_t  packet[]  = {0x01u, 0x02u, 0x03u, 0x04u};
uint32_t expected  = 0xB63CFBCDu;
if (SSFCRC32(packet, sizeof(packet), SSF_CRC32_INITIAL) == expected)
{
    /* Packet integrity confirmed */
}