Using C language to realize parity-check __c language

1. Parity check with C language

unsigned int v;  Number
bool parity = false to be detected;  The initial judgment mark while
(v)
{
parity =!parity;
v = v & (V-1);
}

2. Parity check by building dictionary table:

static const BOOL PARITYTABLE256[256] =
{
# define P2 (n) n, n^1, n^1, n
# define P4 (n) P2 (n), P2 (n^1), P2 (n^1), P2 (n)
# define P6 (n) P4 (n), P4 (n^1), P4 (n^1), P4 (n)
P6 (0), P6 (1), P6 (1), P6 (0)
};
By nesting the macro definition, make a sheet including 0~255 each number contains 1, which contains even number 1, then paritytable256[i]=0, otherwise paritytable256[i]=1;

If you want to determine the parity of the number of I in B of the char type, you can use the following code directly:

unsigned char b;
BOOL parity = paritytable256[b];
For the number of 32-bit, the following code is used:


unsigned int v;
V ^= v >> 16;
V ^= v >> 8;
BOOL parity = paritytable256[v & 0xFF];

Principle:


(1) by v^=v>>16, the lower 16 bits in V are bitwise-or (^) operations, equivalent to the parity of the total   number of 1 in the 0~16 with the total number of digits reserved 1;


(2) through v^=v>>8, a bitwise OR (^) operation of the 9~16 bit in V with the 0~8 bit, equivalent to the parity of the total number of 0~8 bits reserved for 1 and the total number of 1 in the 0~16;


(3) operates through (1) (2). The parity of the total number of 1 in the initial V is the same as the total number of 1 in the 1~8 bit in the last V, and the v&0xff is equivalent to getting 1 of the 1~8 bit in V and then checking the table.


or use the following code:

Unsigned char * p = (unsigned char *) &v;
parity = paritytable256[p[0] ^ p[1] ^ p[ 2] ^ p[3]];
Principle: Take the address of V and make the coercion type to char*,


e.g. v=1234


Binary as:


00000000 0000000000000100 11010010
p[0]:11010010


p[1]:00000100


p[2]:00000000


p[3]:00000000


    ^------------


       11010110


  through p[0] ^ p[1] ^ P[2] ^ P[3] Action, put all 1 in p[i] in a 8-digit number, and then check the table to