1. LC-3 Control Structures
if, else if, while, for, switch

2. If statement Other cases ;if (R1 == R2) ; becomes ;if (R1 < R2)
; if (R1 - R2 != 0) skip code block if true
IFLABEL
NOT R3, R2 ;2’s complement
ADD R3, R3, #1 ;2’s complement
ADD R3, R1, R3 ; evaluate expression
BR?? ENDIFLABEL ; test condition ;{
; if code block ;}
ENDIFLABEL
Other cases
;if (R1 < R2)
; if (R1 - R2 ? 0) skip code block if true;
BR?? ENDIFLABEL ; evaluate NZP bits
;what is the BRxxx to evaluate NZP condition?
;if (R1 > R2)
; if (R1 - R2 ? 0) skip code block if true
BR?? ENDIFLABEL ; evaluate NZP bits;
what does the “?” do in the statement “R1 - R2 ? 0”

3. IF - ELSEIF C Code: if (R1 == R2) { //if code block }
else if ( R1 > R2 ) {
// else if code block
else {
// else code block
Assembly Code: IF
; evaluate R3 <- R2 - R1 to set condition
BR?? ELIF
;{ if code block }
BRNZP ENDIF
ELIF
BR?? ELSE
;{ else if code block }
ELSE
;{ else code block }
ENDIF
What if the evaluation statements are unrelated? i.e.
if (R1 == R2) ; do something
elseif (R1== R3) ; do something different
else ; do something else
endif

4. WHILE LOOP C code: GETC; while ( R0 != ‘\r’) { //loop code block; }
Assembly Code:
GETC
;start of while loop
WHILE
ADD R1, R0, #-10 ; R1 = R0 + #-10
BR? ENDWHILE ; test loop condition
;{ start of loop body
;loop code block
;} end of loop body
BRnzp WHILE
ENDWHILE

5. DO WHILE LOOP C code: do { // loop code block GETC;
} while ( R0 != ‘\r’);
Assembly Code: DO
;{ start of loop
;loop code block
GETC
;} end of loop
AND R1, R0, #-10 ; set condition
BR?? DO ;test loop condition
ENDLOOP ;label not needed

6. FOR LOOP YOUR TURN C code: //for (init, test, next)
for (R1 = -10, R1 > 0, R1--)
{ //start of loop body
//loop code block
} //end of loop body
Assembly Code:
YOUR TURN

7. FOR LOOP C code: //for (init, test, next)
for (R1 = 10, R1 > 0, R1--)
{ //start of loop body
//loop code block
} //end of loop body
Assembly Code:
FOR
AND R1, R1, #0 ; clear R1
ADD R1, R1, #10 ; init statement
FORLOOP
BR? ENDFOR ; test loop condition
;{ start of loop body
;loop code block
;} end of loop body
ADD R1, R1, #-1 ; decrement loop index
BRnzp FORLOOP
ENDFOR

8. SWITCH STATEMENT YOUR TURN C Code: switch (R1) { CASE ‘0’:
; case 0 code block
;break
CASE ‘1’:
; case 1 code block
CASE ‘2’:
; case 2 code block
Default:
; default case code block }
Assembly Code:
YOUR TURN

9. SWITCH STATEMENT Solution #1
Assembly Code:
SWITCH
;Evaluate Test condition Case 0
BRz CASE_0
;Evaluate Test condition Case 1
BRz CASE_1
;Evaluate Test condition Case 2
BRz CASE_2
BRnzp DEFAULT
CASE_0 ;Code block
;Code block
BRnzp ENDSW
CASE_1
CASE_2
DEFAULT
ENDSW
NOT A SOLUTION!!!
WHY WONT THIS WORK?

10. SWITCH STATEMENT Solution #2
Assembly Code:
SWITCH
CASE0 ;
;Evaluate Test condition Case 0
BRnp CASE1
;Code block
BRnzp ENDSW
CASE1 ;
;Evaluate Test condition Case 1
BRnp CASE2
CASE2 ;
;Evaluate Test condition Case 2
BRnp DEFAULT
DEFAULT
ENDSW