Bit Representation

Binary

Decimal -> Binary

One's Complement / Two's Complement

• 为什么这么设计？ CPU处理时不用考虑符号

use 32bits for each number

 1 == 0000 0000 0000 0000 0000 0000 0000 0001

      1111 1111 1111 1111 1111 1111 1111 1110
-1 == 1111 1111 1111 1111 1111 1111 1111 1111  plus 1

Hexadecimal

32-bit signed integer max value = 0x7FFFFFFF

Bit Operation

• & and
• | or
• ~ not
• ^ xor
  • same bits = 0, different bits = 1
• arithmetical shift
  • << left shift
    • add 0 to the right of positive number

  • right shift

    • add 0 to the left of positive number
    • add 1 to the left of negative number
    • 3 >> 1 = 3 / 2 = 1
    • -3 >> 1 = -2 负数除法不建议用位运算做

• logical shift

  • right shift

    • always add 0 to the left of number

bit check

x & (1 << k)

(x >> k) & 1

bit set

x = x | (1 << k)