/* Reference code from RFC1952. Not meant to be used outside test code. */

#include "stm32f4xx_hal.h"


/* Table of CRCs of all 8-bit messages. */
unsigned long crc_table[256];

/* Flag: has the table been computed? Initially false. */
int crc_table_computed = 0;

/* Make the table for a fast CRC. */
void make_crc_table(void)
{
    unsigned long c;

    int n, k;
    for (n = 0; n < 256; n++) {
	c = (unsigned long) n;
	for (k = 0; k < 8; k++) {
	    if (c & 1) {
		c = 0xedb88320L ^ (c >> 1);
	    } else {
		c = c >> 1;
	    }
	}
	crc_table[n] = c;
    }
    crc_table_computed = 1;
}

/*
  Update a running crc with the bytes buf[0..len-1] and return
  the updated crc. The crc should be initialized to zero. Pre- and
  post-conditioning (one's complement) is performed within this
  function so it shouldn't be done by the caller. Usage example:

  unsigned long crc = 0L;

  while (read_buffer(buffer, length) != EOF) {
  crc = update_crc(crc, buffer, length);
  }
  if (crc != original_crc) error();
*/
uint32_t update_crc(uint32_t crc, uint8_t *buf, int len)
{
    unsigned long c = crc ^ 0xffffffffL;
    int n;

    if (!crc_table_computed)
	make_crc_table();
    for (n = 0; n < len; n++) {
	c = crc_table[(c ^ buf[n]) & 0xff] ^ (c >> 8);
    }
    return c ^ 0xffffffffL;
}

/* Return the CRC of the bytes buf[0..len-1]. */
unsigned long crc(unsigned char *buf, int len)
{
    return update_crc(0L, buf, len);
}