Yokogawa Touch Screen GP20 Manuel d'utilisateur télécharger pdf (Page 109)

App-7

IM 04L51B01-17EN

Appendix

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App

Appendix 5 Check Sum Calculation Method

The check sum of binary data is calculated using an algorithm like the one shown below.

int CalcSum(unsigned char *buf, int len)

{

int odd;

unsigned long sum;

unsigned char *p;

sum = 0;

odd = len & 1;

len >>= 1;

for (p = buf ; len ; len --, p += 2)

{

sum += (*p << 8) | *(p + 1);

}

if (odd) sum += (*p << 8);

sum = (sum & 0xffff) + ((sum >> 16) & 0xffff);

if (sum > 0xffff) sum = sum - 0xffff;

return ((~sum) & 0xffff);

}

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