How to pack a 32 bit into 4x8 bit?

Question

I am fairly new to C programming and I am sorry, if the explanation of the problem is unsatisfactory. I have a 32 bit binary number as follows:

typedef unsigned long U32;
U32 a;
a = 11111111000000001111111100000000;

How can I convert that into 4 times 8 bit binary numbers. I just want to take the first 8 bits under a variable and seconds 8 bits into another variable and etc. For example,

typedef uint8;
uint8 b, c, d, e;
b = 11111111;
c = 00000000;
d = 11111111;
e = 00000000;

I made it just for the sake of asking this question. No other reasons. — , Jul 08 '19 at 13:23

progLearner · Answer 1 · 2019-07-11T11:57:47.357

0

You could just apply the correct shift and mask to each variable as per:

typedef unsigned long U32;
U32 a;
a = 0xFF00FF00; //11111111000000001111111100000000;

uint8 b, c, d, e;

e = (uint8)(a & 0xFF);
d = (uint8)((a >> 8) & 0xFF);
c = (uint8)((a >> 16) & 0xFF);
b = (uint8)((a >> 24) & 0xFF);

That is the quick and dirty way. You could also use a loop to be more elegant.

edited Jul 11 '19 at 11:57

answered Jul 08 '19 at 13:10

progLearner

123
10

@progLeaner Is your solution is general or specific to my example? – Jul 08 '19 at 13:55
Will work for any "a" value – progLearner Jul 08 '19 at 14:07
@progLeaner In your answer, you mean the `b` as MSB and `e` as LSB right? Also, can I use the same mechanism to pack 48 bit into a 6x8 bit ? – Jul 11 '19 at 07:07
Yes, same mechanism for 48-bit numbers. I respected the MSB as per your example, so yes b as MSB and e as LSB. – progLearner Jul 11 '19 at 09:32
@progLeaner Which operand to use? I guess the bitwise `&`? You used `&&`. Please correct me if I am wrong. – Jul 11 '19 at 11:10
Yes, that's a typo. Why don't you try and run it in a debugger? – progLearner Jul 11 '19 at 11:57

How to pack a 32 bit into 4x8 bit?

1 Answers1