More chapter 2

• Shift operators
  • sll shift left logical
  • srl shift right logical
  • source register = destination register shifted by immediate
  • This is an r type instruction (surprise)
  • The immediate is between 0 and 31 (why)
  • This uses the shamt field of the r-type instruction
  • Shifting left by i bits is the same as multiplying by 2ⁱ
• And, Or, Not
  • Bitwise boolean operations.
  • Both R and I type.
• Branches
  • beq, bne are the basic instructions.
  • bgt, bge, blt, ble are added as pseudo instructions.
  • To provide the last four an additional instruction is needed. (or instruction family)
  • slt and slti
  • Set less than
  • These are R and I type respectively
  • slt $t0, $t1, $t2
  • If t1 < t2, t0 =1, otherwise t0 = 0
• Jumps
  • jump (j)
    • j imm
    • pc = pc + imm
    • This is a pc relative jump.
    • The range is -2²⁴ to 2^{24-1 words}
    • The top four bits of the PC are added
    • The bottom two bits are set to 0 (word address)
    • See the picture (4.24) page 329
  • jump register (jr)
    • This adds the value of a register to the pc.
    • This is needed for subroutine calls
  • jump and link (jal)
    • This stores the PC+4 into $ra (ok this is a lie, but it will do)
    • And jumps to the immediate as in j
• Building C control structures

  • 	 if condition {
    	     body
             }
    	 

  • 	 branch if condition is false to end
             body
    end:     first instruction past if
    	 

  • 	 if condition {
    	    then-body
    	 } else {
    	    else-body
    	 }
    	 

  • 	 branch if condition is true to then
    	 else body
    	 branch to end
    then:    then body
    end:     first instruction past if
    	 

  •  
    	 while condition  {
    	     body
    	 }
    	 

  • top:
             branch if condition is false to endwhile
    	 body
    	 jump to top
    endwhile:
    	 

  • do while loop?
  • for loop?