misc.

errno

 If you are compiling an application under Linux and get an error message like:
/usr/bin/ld: errno: TLS definition in /lib/libc.so.6 section .tbss mismatches non-TLS reference in ...

The fix is quite simple: explicitly add #include <errno.h> to the offending file and then recompile. 

 

#parity bit

 

7 bits of data	(count of 1-bits)	8 bits including parity
		even	odd
0000000	0	00000000	10000000
1010001	3	11010001	01010001
1101001	4	01101001	11101001
1111111	7	11111111	01111111

The even parity check means the count of bit 1 is even which it includes the even bit, same as for odd parity check.