CODEWITHSUNDEEP
java
08091 Yin
08091 Yin

Reputation: 119

Reading bit inside 2 byte

int id = ((reply[0] & 0x3));
id = (id<<7) | (reply[1] & 0x7F);

Suppose I have a reply array storing 2 byte reply[0] and reply[1]. I wanna read the last two bits in the first byte and all the bits in the second byte, then adding them together

why the code above is going to work, can anyone explain?

Upvotes: 2

Views: 616

Answers (2)

noMAD
noMAD

Reputation: 7844

Convert to binary and you will get your answer. binary of 3 is 11. if you use logical & with 11 you will end up only with the last two bits. That's the answer to your first part.

For the second part, I don't think it will do what you intended it too. You can use logical AND (for carry) and logical XOR to add individual bits.

Try to figure it out ^_^

Upvotes: 1

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726649

This code is not doing what you described: instead of taking the second byte in its entirety, it cuts out its last seven bits (the & 0x7F part; 0x7F is binary 01111111), and concatenates them to the two last two bits of the first number (the << 7 part).

Upvotes: 2

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