CSC373/406: C: Shift Operations [40/42]

• Left Shift: x << y
  • Shift bit-vector x left y positions
    • Throw away extra bits on left
    • Fill with 0’s on right
• Right Shift: x >> y
  • Shift bit-vector x right y positions
    • Throw away extra bits on right
  • Logical shift
    • Fill with 0's on left
  • Arithmetic shift
    • Replicate most significant bit on left
    • Useful with two’s complement integer representation (which we will talk about next week)

Left shift:

 x    == 01100010
 x<<1 == 11000100
 x<<2 == 10001000
 x<<3 == 00010000
 x<<4 == 00100000
 x<<5 == 01000000
 x<<6 == 10000000
 x<<7 == 00000000
 x<<8 == 00000000

Right shift:

        (logical)      (arithmetic)
 x    == 01100010       01100010
 x>>1 == 00110001       00110001
 x>>2 == 00011000       00011000
 x>>3 == 00001100       00001100
 x>>4 == 00000110       00000110
 x>>5 == 00000011       00000011
 x>>6 == 00000001       00000001
 x>>7 == 00000000       00000000
 x>>8 == 00000000       00000000

        (logical)      (arithmetic)
 x    == 11100010       11100010
 x>>1 == 01110001       11110001
 x>>2 == 00111000       11111000
 x>>3 == 00011100       11111100
 x>>4 == 00001110       11111110
 x>>5 == 00000111       11111111
 x>>6 == 00000011       11111111
 x>>7 == 00000001       11111111
 x>>8 == 00000000       11111111