bit extraction from BYTE

[hrishi321]

HI i am using VC++ 2005 I have a BYTE of data, which is of 8 bits 76543210 .....this BYTE consist of 3 fields in it, which are as follows... field 1.... bit 0-3 field 2.... bit 4 field 3.... bit 5 6 7 Now I want to extract all these 3 fields and store in 3 differernt variable.... please provide me an efficient way to do it... thanks in advance

[Cool_Dev]

use logical AND (&) and bit shift operations (<< , >>) in efficient ways..

[normanS]

Read up on unions and structures - that's the elegant way to do it. Bitwise-and and right-shifting (suggested by the previous poster) will also do the job nicely.

[_Superman_]

field1 = (data & 0x0F);
field2 = (data & 0x10) >> 4;
field3 = (data & 0xE0) >> 5;

«_Superman_» I love work. It gives me something to do between weekends.
Microsoft MVP (Visual C++)

[Mohan Ramachandra]

A bit more optimization in field3

«_Superman_» wrote:

field3 = (data & 0xE0) >> 5;

field3 = data>> 5;

[CPallini]

The two different ways (you may find they are translated to the same asm, by the compiler). [update] the first method's asm (SHIFT and AND operator) looks slightly faster)[/update]

struct BitField
{
unsigned int f1:4;
unsigned int f2:1;
unsigned int f3:3;
};

union MyData
{
unsigned char data;
BitField bf;
};

int main(int argc, char *argv[])
{
unsigned char data= rand();

int field1, field2, field3;

// using SHIFT and AND operators
field1 = data & 0xF;
field2 = (data >> 4) & 1;
field3 = data >> 5;

printf("data=%d\n", data);
printf("(1) fields: %d, %d, %d\n", field1, field2, field3);

// using union and bitfield struct
MyData md;
md.data = data;

field1 = md.bf.f1;
field2 = md.bf.f2;
field3 = md.bf.f3;
printf("(2) fields: %d, %d, %d\n", field1, field2, field3);
return 0;
}

:)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]

modified on Wednesday, March 10, 2010 5:31 AM

[_Superman_]

Perfect. :thumbsup:

«_Superman_» I love work. It gives me something to do between weekends.
Microsoft MVP (Visual C++)

[KarstenK]

field 1.... bit 0-3 = > (data & 3) and so on

Press F1 for help or google it. Greetings from Germany

[CPallini]

KarstenK wrote:

field 1.... bit 0-3 = > (data & 3)

field 1.... bit 0-3 = > (data & 15) FFY. :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]

[KarstenK]

"use XYZ in a efficient way" :-O :-O :-O

Press F1 for help or google it. Greetings from Germany