pngcrc.c

#include "pngcrc.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]--the CRC
should be initialized to all 1's, and the transmitted value
is the 1's complement of the final running CRC (see the
crc() routine below)). */

unsigned long update_crc(unsigned long crc, unsigned char *buf, int len)
{
  unsigned long c = crc;
  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;
}

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

unsigned long arrayToCRC(unsigned char *array)
{
  unsigned long output = 0;
  int i = 0;

  for (i = 0; i<4; i++)
  {
    output = output << 8;
    output = output | array[i];
  }

  return output;
}