Assembly Language Programming - Fundamentals of Computer Organization and Architecture - page 53

TABLE 3.13 Sample of the X86 Processor Control Instructions

Mnemonic Operation Subtype

HLT Halt External sync

LOCK Lock the bus External sync

CLC Clear carry flag Flag

CLI Clear interrupt flag Flag

STI Set interrupt flag Flag

INVD Invalidate data cache General control

defined as an array of N elements each of size byte. FLAG is a memory variable used
to indicate whether the list has been sorted or not. The register CX is used as a coun-
ter with the Loop instruction. The Loop instruction decrements the CX register and
branch if the result is not zero. The addressing mode used to access the array List
[BX þ

1] is called based addressing mode. It should be noted that since we are
using BX and BX

þ 1 the CX counter is loaded with the value 999 in order not to

exceed the list.

MOV CX, 1000 2 1 ; Counter ¼ CX (1000 2 1)
MOV BX, Offset LIST ; BX pointer to LIST
CALL SORT
.....

SORT PROC NEAR

Again: MOV FLAG, 0 ; FLAG 0

Next: MOV AL, [BX]

CMP AL, [BX þ 1] ;Compare current and next values
JLE Skip ;Branch if current , next values
XCHG AL, [BX þ 1] ;If not, Swap the contents of the
MOV [BX þ 1], AL

;current location with the next one

MOV FLAG, 1 ;Indicate the swap

Skip: INC BX ; BX BX þ 1

LOOP Next ;Go to next value

CMP FLAG, 1 ;Was there any swap

JE Again ;If yes Repeat process

RET

SORT ENDP

Example 4 Here we implement the SEARCH algorithm in the 8086 instruction

set. LIST is defined as an array of N elements each of size word. FLAG is a
memory variable used to indicate whether the list has been sorted or not. The register
CX is used as a counter with the loop instruction. The Loop instruction decrements