/* ================================================================
Checksum functionality
----------------
checksum.cpp/checksum.hpp provide functionality for checking and generating checksums.
================================================================ */
#include "checksum.hpp"
#include <stdio.h>

uint32_t crc32(uint32_t crc, const char *buf, size_t len) {
  static uint32_t table[256];
  static int table_gen = 0;
  uint32_t word;
  uint8_t octet;
  int i, j;
  const char *p, *q;
  // Generate our table if not yet generated
  if (table_gen == 0) {
    for (i = 0; i < 256; i++) {
      word = i;
      for (j = 0; j < 8; j++) {
        if (word & 1) {
          word = (word >> 1) ^ 0xedb88320;
        } else {
          word >>= 1;
        }
      }
      table[i] = word;
    }
    table_gen = 1;
  }
  // Generate our CRC32!
  crc = ~crc;
  q = buf + len;
  for (p = buf; p < q; p++) {
    octet = *p;
    crc = (crc >> 8) ^ table[(crc & 0xff) ^ octet];
  }
  return ~crc;
}