MIPS Assembly

By : ATHIRAH BT ZAHARUDIN

MIPS Assembly Arithmetics Instruction

All arithmetic and logical instructions have 3 operands
Operand order is fixed (destination first):
       <opcode>   <dest>, <src1>, <src2>

Example:

       C code:      a = b + c;
   
      MIPS ‘code’: add a, b, c

“The natural number of operands for an operation like addition is three…requiring every 
instruction to have exactly three operands, no more and no less, conforms to the 
philosophy of keeping the hardware simple”



Assembly Arithmetic Instructions


Design Principle:  simplicity favors regularity.


Of course this complicates some things...
                 
                 C code:                              a = b + c + d;
                 MIPS pseudo-code:              add a, b, c
                                                          add a, a, d
Operands must be registers (or immediates), only 32 registers are provided 
Design Principle:  smaller is faster.

addi

addiu

addu

div

mult

multu

sub

subu

...

Immediates

In MIPS assembly, immediates are literal constants.

Many instructions allow immediates to be used as parameters.

                            addi $t0, $t1, 42  # note the opcode

                            li $t0, 42       # actually a pseudo-instruction

Note that immediates cannot be used with all MIPS assembly instructions; refer to your 

MIPS reference card.

Immediates may also be expressed in hexadecimal:  0xFFFFFFFF

MIPS Assembly Logical Instructions

Logical instructions also have 3 operands:
    <opcode>   <dest>, <src1>, <src2>

Examples:
            and $s0, $s1, $s2   # bitwise AND
            andi $s0, $s1, 42
            or  $s0, $s1, $s2   # bitwise OR
            or  $s0, $s1, $s2   # bitwise OR
            ori $s0, $s1, 42
            nor $s0, $s1, $s2   # bitwise NOR (i.e., NOT OR)
            sll $s0, $s1, 10      # logical shift left
            srl $s0, $s1, 10     # logical shift right

QTP: MIPS assembly doesn’t include the logical operation not. 




Assembly Load and Store Instructions


Transfer data between memory and registers

 Example:

             C code:        A[12] = h + A[8];
             MIPS code:    lw $t0, 32($s3)   # load word
                                add $t0, $s2, $t0
                                sw $t0, 48($s3)   # store word

Can refer to registers by name (e.g., $s2, $t2) instead of number
Load command specifies destination first: opcode <dest>, <address>
Store command specifies destination last: opcode <dest>, <address>

Remember arithmetic operands are registers or immediates, not memory!
Can’t write:   add 48($s3), $s2, 32($s3)




Addressing Modes


In register mode the address is simply the value in a register:

lw $t0, ($s3)

In immediate mode the address is simply an immediate value in the instruction:

lw $t0, 0

In base + register mode the address is the sum of an immediate and the value in a 
register:
          lw $t0, 100($s3)

There are also various label modes:

                                                    j absval

                                                    j absval + 100
                                                j absval + 100($s3)

Calculation

MIPS
- loading words but addressing bytes
- arithmetic on registers only

# Instruction              # Meaning
add $s1, $s2, $s3        #  $s1 = $s2 + $s3
sub $s1, $s2, $s3        #  $s1 = $s2 – $s3
sub $s1, $s2, $s3        #  $s1 = $s2 – $s3
lw $s1, 100($s2)        #  $s1 = Memory[$s2+100]
sw $s1, 100($s2)        #  Memory[$s2+100] = $s1

HERE IS THE MIPS REFERENCE DATA

Below is the CPU Arithmetics Instruction

ADD      Add Word
ADDI     Add Immediate Word
ADDIU   Add Immediate Unsigned Word
ADDU    Add Unsigned Word
CLO      Count Leading Ones in Word
CLZ      Count Leading Zeros in Word
DIV       Divide Word
DIVU     Divide Unsigned Word
MADD   Multiply and Add Word to Hi, Lo
MADDU Multiply and Add Unsigned Word to Hi, Lo
MSUB    Multiply and Subtract Word to Hi, Lo
MSUBU  Multiply and Subtract Unsigned Word to Hi, Lo
MUL     Multiply Word to GPR
MULT   Multiply Word
MULTU Multiply Unsigned Word
SEB     Sign Extend Byte
SEH     Sign Extend Halfword
SLT     Set on Less Than
SLTI    Set on Less Than Immediate
SLTIU  Set on Less Than Immediate Unsigned
SLTU   Set on Less Than Unsigned
SUB     Subtract Word
SUBU   Subtract Unsigned Word

MIPS INSTRUCTION SET