Hexadecimal comparison for big number in c program - c

Question

#include<stdio.h>
long long int A = 0xAABBCCDDBBCCFFEE;
long long int B = 0xAACCCCDDBBDDFF00;
int array[8] = {'\0'};
int byte_compare(int A, int B)
{
int i = 0;
long long int j = 0xFF;
long long int C = A;
long long int D = B;
while(i < 8)
{
C = (j & A);
D = (j & B);
printf("C = %x\n",C);
printf("D = %x\n",D);
printf("j = %x\n",j);
if(C == D)
{
array[i] = 1;
}
else
{
array[i] = 0;
}
i++;
j = j << 8;
}
}
main()
{
int i = 0;
byte_compare(A,B);
while(i < 8)
{
printf("array[%d] - %d\n",i, array[i]);
i++;
}
}
long long int A = 0xAABBCCDDBBCCFFEE;
long long int B = 0xAACCCCDDBBDDFF00;
result = 10111010
when A and B byte number matches with each other it should print 1 otherwise 0.
for my above program it is printing output
C = ee
D = 0
j = ff
C = ff00
D = ff00
j = ff00
C = cc0000
D = dd0000
j = ff0000
C = bb000000
D = bb000000
j = ff000000
C = 0
D = 0
j = 0
C = 0
D = 0
j = 0
C = 0
D = 0
j = 0
C = 0
D = 0
j = 0
array[0] - 0
array[1] - 1
array[2] - 0
array[3] - 1
array[4] - 1
array[5] - 1
array[6] - 1
array[7] - 1
Not able to compare after first four byte please help me what datatype I should use instead above.

Answer 1

You have many problems in your code
#include <stdio.h>
#include <stdint.h>
#include <inttypes.h>
void byte_compare(uint64_t C, uint64_t D, int *array)
{
int i = 0;
while (i < 8)
{
printf("C = %"PRIx64"\n" , (C&0xFF));
printf("D = %"PRIx64"\n\n", (D&0xFF));
if ((C&0xFF) == (D&0xFF))
{
array[i] = 1;
}
else
{
array[i] = 0;
}
i++;
C >>= 8;
D >>= 8;
}
}
int main(void)
{
int i = 0;
uint64_t A = UINT64_C(0xAABBCCDDBBCCFFEE);
uint64_t B = UINT64_C(0xAACCCCDDBBDDFF00);
int array[8] = {0};
byte_compare(A, B, array);
while (i < 8)
{
printf("array[%d] - %d\n", i, array[i]);
i++;
}
}
Correct type for your variables must be unsigned long long due to the literals: bit 63 is set to 1 so assign it to a signed variable causes overflow which invoke UB. Using stdint.h standard header you can use uint64_t that is clearer.
byte_compare function definition is wrong, you must pass parameters with correct type: unsigned long long (uint64_t). Moreover the function does not return an int so should be void.
printf with %x format specifier wants an unsigned int, not a uint64_t. Best thing to do is to use defined in inttypes.h standard header where all format specifier are well reported: in your case PRIx64 is the right one.
In your version of code you are left shifting a long long int that is used as mask to "select" the byte to check. It is plain wrong because last shift causes an overflow on a signed value that is UB as for point 1.
stdint.h has also macros that append the correct suffix to literals.
Another example using a mask:
#include <stdio.h>
#include <stdint.h>
#include <inttypes.h>
void byte_compare(uint64_t C, uint64_t D, int *array)
{
uint64_t mask = UINT64_C(0xFF00000000000000);
while (mask > 0)
{
printf("C = %"PRIx64"\n" , (C&mask));
printf("D = %"PRIx64"\n\n", (D&mask));
if ((C&mask) == (D&mask))
{
*array = 1;
}
else
{
*array = 0;
}
mask >>= 8;
array--;
}
}
int main(void)
{
int i = 0;
uint64_t A = UINT64_C(0xAABBCCDDBBCCFFEE);
uint64_t B = UINT64_C(0xAACCCCDDBBDDFF00);
int array[8] = {0};
byte_compare(A, B, &array[7]);
while (i < 8)
{
printf("array[%d] - %d\n", i, array[i]);
i++;
}
}