Addition and Subtraction Instructions

The following table lists some addition and subtraction instructions. They are with the R-type format and include:

Signed Addition & Subtraction Addition & Subtraction without Overflow 
 add  rd, rs, rt    # rd: destination register
 sub  rd, rs, rt    # rs: 1st source register
 neg  rd, rs        # rt: 2nd source register
 
 addu  rd, rs, rt
 subu  rd, rs, rt

The addition performs the 2’s complement operation between the two source registers (rs and rt), and places the result in the destination rd.
add rd, rs, rt         # add with overflow
Computes the two’s complement sum of two signed values. It adds the contents of rs to the contents of rt, or it can add the contents of rs to the immediate value. Add (with overflow) puts the result in the destination register. When the result cannot be extended as a 32-bit number, the machine signals an overflow exception.
add (register) add (immediate) Integer 7 to Char '7' 
     .data
 X:  .byte   10
 Y:  .word  -20

     .text 
     lb   $t0, X
     lw   $t1, Y
     add  $a0, $t0, $t1
     li   $v0, 1
     syscall
 
     .data
 X:  .byte  10 

     .text 
     lb   $t0, X 
     add  $a0, $t0, -20
     li   $v0, 1
     syscall
 
     .data
 i:  .byte   7 
 s:  .space  1
     .byte   0

     .text 
     lb  $t0, i
     
     sb  $t0, s    
     la  $a0, s 
     li  $v0, 4
     syscall
Output Output Output







7 ('7')