Not quite clear

[KingoftheWorld]

Hi All,

I am not quite clear understanding what the C macro below do:

#define BIT(word, i) (((word) & 1 << (i)) >> (i))

/* Pass data into BIT macro */

BIT(0x00FF, 5);

Thanx for any detail explanation for above code.

KW

[quzah]

Given a value 'word', and a number 'i', do the following:

Shift the value of 1 'i' places to the left.
Use a bitwise AND to see if that bit is set on the value 'word'.

Take the result of that & operation, and shift it back 'i' places.

Thus:

0001000100010001

Let's say we check the 5th place.

10000

0001000100010001 & 10000

Thus, we have a "true", or a 1.

10000 >> 5 times is 1

In a nutshell, it just tests to see if a single bit is set, and it returns a "true" or "false" (a 1 or a 0). There really is no point in going through the additionall right shifts. Just test your value for zero, and if it's not zero, the value is set.

Quzah.

[KingoftheWorld]

Thanks! quzah.

KingogtheWorld
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