Grabbing n bits from a byte

Question

I\'m having a little trouble grabbing n bits from a byte.

I have an unsigned integer. Let\'s say our number in hex is 0x2A, which is 42 in decimal. In binary it looks li

Answer 1

"grabbing" parts of an integer type in C works like this:

1. You shift the bits you want to the lowest position.
2. You use & to mask the bits you want - ones means "copy this bit", zeros mean "ignore"

So, in you example. Let's say we have a number int x = 42;

first 5 bits:

(x >> 3) & ((1 << 5)-1);

or

(x >> 3) & 31;

To fetch the lower three bits:

(x >> 0) & ((1 << 3)-1)

or:

x & 7;