logical instructions

Complete

Summary

Shift left logical

  • R-type
  • multiply by 2ⁿ
  • n is a 5-bit unsigned number
mips
sll dest, src, n # dest <- src << n

5 bits since the max that ever needs to be shifted is

Shift right logical

  • R-type
  • multiply by 2⁻ⁿ
  • n is a 5-bit unsigned number
mips
srl dest, src, n # dest <- src >> n

AND

  • R-type
  • bitwise AND
mips
and dest, src1, src2 # dest <- src1 & src2

AND immediate

  • I-type
mips
andi dest, src, n # dest <- src & n

OR

  • R-type
  • bitwise OR
mips
or dest, src1, src2 # dest <- src1 | src2

OR immediate

  • I-type
mips
ori dest, src, n # dest <- src | n

NOR

  • R-type
mips
nor dest, src1, src2 # dest <- ~(src1 | src2)

no nori instruction since there is not much need for it

XOR

  • R-type
mips
xor dest, src1, src2 # dest <- src1 ^ src2

XOR immediate

  • I-type
mips
xori dest, src, n # dest <- src ^ n

NOT

  • pseudo-instruction
  • can be made from NOR
mips
not dest, src # dest <- ~src

# is translated to
nor dest, src, $zero # dest <- ~(src | 0)

Concept

Loading 32-bit numbers

  • only using immediate instructions
  • load the upper 16-bits, then set the lower 16-bits
mips
lui dest, n # dest <- n << 16
ori dest, src, x # dest <- src | x

Application

Masking

  • preserve select bits, discard the rest
mips
andi $t0, $t0, 0xFFF

Loading a 32-bit number

mips
lui $t0, 0xAAAA # 1010 1010 1010 1010
ori $t0, $t0, 0xF0F0 # 1111 0000 1111 0000
# 1010 1010 1010 1010 1111 0000 1111 0000

XOR for selective inversion

while AND can be used to select bits, XOR can invert a selection of bits