C位操作

Question

I have to accomplish bit manipulation.

My task is to iterate through many one byte values, and pull out certain amount of bits from each byte (sometimes odd, sometimes even) and be able to combine all those together. Is there a good way to accomplish this?

Here's a better explanation. My goal is to allow me to take certain bits from one byte and combine them with bits from another byte.

So for example, combine the first 3 bits from 0xE1, with the last 5 bits from 0xA1.

Answer 1

Extracting bits from integral values can be done with the bitwise and and shift operations.

unsigned int c = 23;

c & 0xF  // extract the lowest 4 bits, 0xF is binary 1111
c & 0x7F // extract the lowest 7 bits, 0x7F is binary 1111111
(c >> 4) & 0x3 // extract 2 bits starting at bit 4 (0 indexed).