source: abuse/trunk/src/crc.cpp @ 57 Tweet

/*
 *  Abuse - dark 2D side-scrolling platform game
 *  Copyright (c) 1995 Crack dot Com
 *
 *  This software was released into the Public Domain. As with most public
 *  domain software, no warranty is made or implied by Crack dot Com or
 *  Jonathan Clark.
 */

#include "config.h"

#include "crc.hpp"

uint16_t calc_crc(uint8_t *buf, int len)
{
  uint8_t c1=0,c2=0;
  while (len)
  {
    len--;
    c1+=*buf; 
    c2+=c1;
    buf++;
  }
  return (c2<<8)|c1;
}


 
uint32_t crc_file(bFILE *fp)
{
  uint8_t crc1=0,crc2=0,crc3=0,crc4=0;

  int size=0x1000;
  uint8_t *buffer=(uint8_t *)jmalloc(size,"crc_buffer"),*c;
  long l=fp->file_size();
  long cur_pos=fp->tell();
  fp->seek(0,0);
  while (l)
  {
    int nr=fp->read(buffer,size);
    if (nr==0) l=0;
    else
    {
      l-=nr;
      for (c=buffer;nr;nr--,c++)
      {      
        crc1+=*c;
        crc2+=crc1;
        crc3+=crc2;
        crc4+=crc3;
      }
    }
  }
  fp->seek(cur_pos,0);
  jfree(buffer);
  return (crc1|(crc2<<8)|(crc3<<16)|(crc4<<24));
}