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 #include #include 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...