PJON_CRC32.h

#pragma once
 
/* CRC32 table-less implementation
   See: http://www.hackersdelight.org/hdcodetxt/crc.c.txt
 
  Polynomial
 
  0x82608edb = x^32+x^26+x^23+x^22+x^16+x^12+x^11+x^10+x^8+x^7+x^5+x^4+x^2+x+1
  (0x82608edb; 0x104c11db7) <=> (0xedb88320; 0x1db710641)
                                    |
                                  bit-reversed polynomial implicit +1 notation
                                  or reverse reciprocal notation */
 
struct PJON_crc32 {
 
    static inline uint32_t compute(
        const uint8_t *data,
        uint16_t length,
        uint32_t previousCrc32 = 0
    )
    {
        uint8_t bits;
        uint32_t crc = ~previousCrc32; // same as previousCrc32 ^ 0xFFFFFFFF
        uint8_t * current = (uint8_t*) data;
        while(length--) {
            crc ^= *current++;
            bits = 8;
            while(bits--) {
                if(crc & 1) {
                    crc = (crc >> 1) ^ 0xEDB88320;
                } else {
                    crc =  crc >> 1;
                }
            }
        }
        return ~crc; // same as crc ^ 0xFFFFFFFF
    };
 
 
    static inline bool compare(
        const uint32_t computed,
        const uint8_t *received
    )
    {
        for(uint8_t i = 4; i > 0; i--)
            if(
                (uint8_t)(computed >> (8 * (i - 1))) !=
                (uint8_t)(received[3 - (i - 1)])
            ) {
                return false;
            }
        return true;
    };
 
};