Programming Languages - Bit and Byte

Bit

• the most basic unit of computing
• binary: either 0 or 1

AND(&)

| AND | 0   | 1   |
| --- | --- | --- |
| 0   | 0   | 0   |
| 1   | 0   | 1   |

OR(|)

| OR  | 0   | 1   |
| --- | --- | --- |
| 0   | 0   | 0   |
| 1   | 0   | 1   |

XOR(^)

| XOR | 0   | 1   |
| --- | --- | --- |
| 0   | 0   | 0   |
| 1   | 0   | 1   |

NOT(!)

| NOT |     |
| --- | --- |
| 0   | 1   |
| 1   | 0   |

Basic Operations

Bitwise And: &

int bitmask = 0x000F;
int val = 0x2222;

System.out.println(val & bitmask);
// 2

Bitwise exclusive OR: ^

Bitwise inclusive OR: |

Unary bitwise complement: ~

System.out.println(~256);
// -257

Signed left shift: <<

Signed right shift: >>

Unsigned right shift: >>>

Byte

• 1 byte = 8 bits = 2 hex character
• another name: octet
• historically, 1 byte(8 bits) is used to encode a single character. ASCII uses 7 bits, 256 code points, more than enough for English characters(both lowercase and uppercase). One extra bit can be used as a parity bit.
• now one character may need more than one byte to store, depend on the encoding.
• in C/C++, byte ranges from 0 to 255
• in Java, byte is signed: -127 to 128

Summary

• bit: naked 0s and 1s
• byte: grouped as 8 bits, still naked 0s and 1s, depend on how do you interpret it.