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/* authparity.c,v 3.1 1993/07/06 01:07:55 jbj Exp
* auth_parity - set parity on a key/check for odd parity
*/
#include "ntp_stdlib.h"
int
DESauth_parity(key)
U_LONG *key;
{
U_LONG mask;
int parity_err;
int bitcount;
int half;
int byte;
int i;
/*
* Go through counting bits in each byte. Check to see if
* each parity bit was set correctly. If not, note the error
* and set it right.
*/
parity_err = 0;
for (half = 0; half < 2; half++) { /* two halves of key */
mask = 0x80000000;
for (byte = 0; byte < 4; byte++) { /* 4 bytes per half */
bitcount = 0;
for (i = 0; i < 7; i++) { /* 7 data bits / byte */
if (key[half] & mask)
bitcount++;
mask >>= 1;
}
/*
* If bitcount is even, parity must be set. If
* bitcount is odd, parity must be clear.
*/
if ((bitcount & 0x1) == 0) {
if (!(key[half] & mask)) {
parity_err++;
key[half] |= mask;
}
} else {
if (key[half] & mask) {
parity_err++;
key[half] &= ~mask;
}
}
mask >>= 1;
}
}
/*
* Return the result of the parity check.
*/
return (parity_err == 0);
}
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