#include <stdio.h>

unsigned long CRCTable[256];
int CRCTable_initialized=0;

#define CRC32_POLYNOMIAL     0xEDB88320L

void CRCTable_Init(){
    int i;
    int j;
    unsigned long crc;

	if(CRCTable_initialized){
		return;
	}
	CRCTable_initialized=1;

    for (i=0;i<256;i++){
        crc=i;
        for (j=8;j>0;j--){
            if (crc&1)
                crc=(crc>>1)^CRC32_POLYNOMIAL;
            else
                crc>>=1;
        }
        CRCTable[i]=crc;
    }
}


unsigned long CRC_Buffer(unsigned char *buffer,int len,unsigned long crc){
    unsigned char *p;
    unsigned long temp1;
    unsigned long temp2;

	// Calcular CRC del buffer
	p=(unsigned char*)buffer;
	while(len--!=0) {
		temp1=(crc>>8)&0x00FFFFFFL;
		temp2=CRCTable[((int)crc^*p++)&0xff];
		crc=temp1^temp2;
	}

	return(crc);
}


unsigned long CRC_File(FILE *file){
    unsigned long crc;
    int count;
    unsigned char buffer[512];
    unsigned char *p;
    unsigned long temp1;
    unsigned long temp2;

	CRCTable_Init();

    crc=0xFFFFFFFFL;
    for(;;){
		// Llenar el buffer
        count=fread(buffer,1,512,file);
        if(count==0)
            break;

		// Calcular CRC del buffer
		crc=CRC_Buffer(buffer,count,crc);
    }
    return(crc^=0xFFFFFFFFL);
}