Low Level Bit Hacks You Absolutely Must Know

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March 02, 2010, 19:11

IMHO, it's better if you don't set things on the macros unless it's necessary. It makes code more readable and allows composing the macros. For example the "rightmost off" one, as Peter Kankowski said, can be composed to make a power of 2 test.

B_TURNOFF_1(n); /* Did n change? */

#define RIGHTMOST_OFF(x) ((x) & ((x)-1))
#define IS_POW2(x) (RIGHTMOST_OFF(x)==0)

i = RIGTMOST_OFF(i); /* More readable */
if (IS_POW_2(j)) {
/* do something */
}

My $.02

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