BINSRC.ASM

RETURN MACRO
	MOV AH, 4CH
	INT 21H
ENDM

WRITE MACRO VAR
	LEA DX, VAR
	MOV AH, 09H
	INT 21H
ENDM

.MODEL SMALL
.DATA
	ARR DW 1, 4, 9, 16, 25
	N DW ($ - ARR) / 2
	KEY EQU 15
	KEYF DB 'Key was found.', 10, 13, '$'
	KEYNF DB 'Key was not found.', 10, 13, '$'

    
.CODE
	MOV AX, @DATA
	MOV DS, AX
    
	MOV AX, 0
	MOV BX, N
	DEC BX
BINSRC:

	CMP AX, BX
	JG NOTFOUND
	
	MOV CX, BX
	ADD CX, AX
	SAR CX, 1

	MOV SI, CX
	ADD SI, SI	;IN WORD OPERATIONS,  MID POSITION IS TWICE AS EXPECTED

	MOV DX, KEY
	CMP DX, ARR[SI]
	JE FOUND
	JL LEFT
	JG RIGHT

	LEFT:
		SUB CX, 1
		MOV BX, CX
		JMP BINSRC
	RIGHT:
		ADD CX, 1
		MOV AX, CX
		JMP BINSRC
	FOUND:
		WRITE KEYF
		RETURN
		JMP EOF
	NOTFOUND:
		WRITE KEYNF
		RETURN
	EOF: END