STM32F0 CRC32, supports unaligend memory as input.

crc.c

/*
 * Resource used:
 * CRC32 peripheral
 */

#include "crc.h"

#include "stm32f0xx_ll_bus.h"

void crc32_init(void) {
    // Enable CRC32's clock
    LL_AHB1_GRP1_EnableClock(LL_AHB1_GRP1_PERIPH_CRC);
    crc32_reset();
}

void crc32_reset(void) {
    CRC->CR = 0xE1; // Reverse output data, Reverse input data by word, Reset, RM0091 Page 224.
    while (CRC->CR & 1);
}

void crc32_hash(const void* addr, size_t len) {
    void* end_addr = (void*) (((uint32_t)addr >> 2) << 2);
    if (addr != end_addr) {
        // Align the head to 4-byte boundary
        end_addr = (void*) ((char*)end_addr + 4);
        while (len > 0 && addr < end_addr) {
            crc32_hash8(*((const char*)addr));
            addr++;
            len--;
        }
    }

    // addr is now aligned to 4-byte boundary
    end_addr = (void*) ((uint32_t)addr + ((len >> 2) << 2));
    while (addr < end_addr) {
        crc32_hash32(*((const uint32_t*)addr));
        addr += 4;
        len -= 4;
    }

    // Hash the tailing bytes (less than 4), if any
    while (len > 0) {
        crc32_hash8(*((const char*)addr));
        addr++;
        len--;
    }
}

uint32_t crc32_calc(const void* addr, size_t len) {
    crc32_reset();
    crc32_hash(addr, len);
    return crc32_result();
}

crc.h

#ifndef CRC_H_
#define CRC_H_

#include <stdint.h>
#include <stddef.h>

#define crc32_hash8(dat) (*(((uint8_t*)(&(CRC->DR)))) = dat)
#define crc32_hash16(dat) (*(((uint16_t*)(&(CRC->DR)))) = dat)
#define crc32_hash32(dat) (*(((uint32_t*)(&(CRC->DR)))) = dat)
#define crc32_result() (CRC->DR ^ 0xFFFFFFFF)

void crc32_init(void);

void crc32_reset(void);

/**
 * Hash the bytes in the buffer.
 * This function handles unaligned access.
 * The algorithm is compatible with USB-PD.
 *
 * Steps are:
 * 1. Call crc32_reset() to reset the CRC32 peripheral into
 *    its default state (clear the previous result).
 * 2. Call crc32_hash() as many times as needed.
 * 3. Invoke crc32_result() to get the CRC32 result.
 */
void crc32_hash(const void* addr, size_t len);

/*
 * A wrapper of the above steps.
 */
uint32_t crc32_calc(const void* addr, size_t len);

#endif /* CRC_H_ */