Figure 3-39 Loop instructions.
| Name | Mnemonic and Format | Alternate Mnemonic | Test Condition* | |||
|---|---|---|---|---|---|---|
| Loop | LOOP OPR | (CX) != 0 | ||||
| Loop while zero, or equal | LOOPZ OPR | LOOPE | ZF = 1 and (CX) != 0 | |||
| Loop while nonzero, or not equal | LOOPNZ OPR | LOOPNE | ZF = 0 and (CX) != 0 | |||
| Branch on CX | JCXZ OPR | (CX) = 0 | ||||
*Except for JCXZ which leaves (CX) unchanged, (CX) | ||||||
Flags: No flags are affected. | ||||||
Addressing modes: Mode is relative to IP. OPR must represent a label that is within -128 to 127 bytes of the instruction following the loop instruction. | ||||||
Figure 3-40 Program for adding an array of binary numbers.
| Data related directives, input, and other code M, ARRAY, and TOTAL are defined as word variables MOV CX,M ;PUT COUNT IN CX
MOV AX,0 ;ZERO AX
MOV SI,AX ;AND SI
START_LOOP: ADD AX,ARRAY[SI] ;ADD NEXT ELEMENT TO AX
ADD SI,2 ;INCREMENT INDEX BY TWO
LOOP START_LOOP ;REPEAT LOOP IF CX NONZERO
MOV TOTAL,AX ;STORE RESULT IN TOTAL
Output and other code |
Figure 3-42 Search example using LOOPNE.
| Data related directives, input, and other code L is defined as word variable and ASCII_STR is defined as byte variable MOV CX,L ;PUT ARRAY SIZE IN CX
MOV SI,-1 ;INITIALIZE INDEX, AND
MOV AL,20H ;PUT CODE FOR SPACE IN AL
NEXT: INC SI ;INCREMENT INDEX
CMP AL,ASCII_STR[SI] ;TEST FOR SPACE
LOOPNE NEXT ;LOOP IF NOT SPACE AND COUNT IS NONZERO
JNZ NOT_FOUND ;IF SPACE NOT FOUND, BRANCH TO NOT_FOUND
Output and other code |
Figure 3-35 Branch address computation using 16-bit displacement.
This is page 36.
(CX)-1. Then if the test condition is met, (IP)