Campbell BMP5 Información técnica descargar pdf (Pagina 64)

Appendix B. Calculating Packet Signatures and the Signature Nullifier

B-2

uint2 new_seed = (sig << 1)&0x1FF;

byte null1;

uint2 new_sig = sig;

if(new_seed >= 0x0100)

new_seed++;

null1 = (byte)(0x0100 - (new_seed + (sig >> 8)));

new_sig = calcSigFor(&null1,1,sig);

// now perform the same calculation for the most significant byte

// in the signature. This time we will use the signature that was

// calculated using the first null byte

byte null2;

new_seed = (new_sig << 1)&0x01FF;

if(new_seed >= 0x0100)

new_seed++;

null2 = (byte)(0x0100 - (new_seed + (new_sig >> 8)));

// now form the return value placing null in the most

// significant byte location

uint2 rtn = null1;

rtn <<= 8;

rtn += null2;

return rtn;

}// calcSigNullifier

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Campbell BMP5 Información técnica Pagina 64