Crc-128 bits source code in c++

Thank you very much for your fast answer, I have already been reading that link, but It is not suitable for my development.

I have an unsigned char message[256] (including the crc-128 (16 last bytes of message) and I need to check that this crc is correct.

I have to implement the ekms crc-128 but I can't find any information about it. I only have the polinomial but I don't know how to obtain the crc.
I have found this example (that appears like a generic crc implementation) but I have many problems with the lenght of data (which C++ type do I have to use for the polinomial, and how can I do the mathematical operations with it?): This example is a CRC-16 (I think)


#include <stdio.h>
#include <string.h>
#include <stdlib.h>

void calcula_crc(unsigned longitud, BYTE *mensaje, BYTE *crc)
{
/* polinomio generador */
char polinomio[] = {1,0,0,0,0,1,0,0,0,0,0,0,1,0,0,0};

/* variables */
unsigned long resultado = -1;
char ctl;
int i,j,k;

/* bucle principal para el calculo del CRC */
for(i = 0; i < longitud; i++)
{
for(j = 0; j < 8; j++)
{
ctl = (resultado & 1) ^ ((mensaje >> j) & 1);
resultado = (resultado & ~1) >> 1;

for(k = 0; k < sizeof(polinomio); k++)
{
if(ctl && polinomio[sizeof(polinomio) - 1 - k])
resultado ^= (unsigned long) 1 << k;
}
}
}

/* pone a cero los bits del resultado no ocupados por el CRC */
for(i = sizeof(polinomio); i < sizeof(resultado) * 8; i++)

resultado |= (unsigned long) 1 << i;

/* devuelve el CRC de la secuencia */
resultado = ~resultado;
resultado >>= 16;
crc[0] = resultado & 0xff;
crc[1] = (resultado >> 8) & 0xff;
}


Thank you in advance everybody, I am a bit desperate...