primes.asm

; PROGRAM TO GET FIRST N NO OF PRIMES

;including the macro file
include macros.inc

data segment

cr      equ     0dh             ;ASCII code for carriage return
lf      equ     0ah             ;ASCII code for line feed

msg1    DB      'HOW MANY PRIMES TO BE PRINTED:$'
MSG2    DB      CR,LF,'PRIME SERIES:','$'
PRIME   DW      100     DUP ( 0 )          ;PRIME ARRAY


NUM     DB      ?
NEWLINE DB      CR,LF,'$'
RESULT  DB      20 DUP ( '$' )


data ends

CODE    SEGMENT   
        ASSUME  CS:CODE,DS:DATA


PRIMES: 
        MOV AX,DATA
        MOV DS,AX

        ;READ PRIME COUNT
        prints msg1
        readi num

        ;INITIALIZE PRIME(0)=1 , PRIME(1) =2

        MOV SI,OFFSET PRIME     ;SI = TABLE ADDRESS
        MOV DX,1
        MOV WORD PTR [SI],DX    ;PRIME(0)=0   ;WE CHANGE HERE

        ADD SI,02               ;SI POINTS TO WORD ARRAY
        INC DX
        MOV WORD PTR [SI],DX   ;PRIME(1)=1


        ;CX =NUMBER OF PRIMES

        MOV CH,00
        MOV CL,NUM

        ;PRIME GENERATION COUNT

        MOV BX,2

        ;PRIME SERIES GENERATION

NEXTPRIME:
        ;TO DECIDE PRIME, DIVIDE BY 2..(N-1)
        ;IF ANY WHERE INTEGER DIVISION IS PERFORMED
        ;THEN NUMBER IS NOT PRIME
        MOV DH,02H      ;DIVIDED NUMBER=2
        INC DL          ;NEXT NUMBER

NEXTCHECK:
        MOV AH,00
        MOV AL,DL
        DIV DH          ;NUMBER/DH

        CMP AH,00       ;IF REMINDER = O THEN NOT PRIME
        JE NOTPRIME
        INC DH          ;NEXT DIVIDED TERM
        CMP DH,DL       ;CHECK WHETHER TERM < NUMBER
        JL NEXTCHECK    ;IF YES THEN NEXTCHECK

        ;NUMBER IS PRIME SO STORE THAT IN A PRIME TABLE

        MOV AH,00
        MOV AL,DL

        ADD SI,02       ;ADJUST SI FOR PRIME(I)
        MOV WORD PTR [SI],AX
        INC BX          ;INCREMENT PRIME COUNT

NOTPRIME:
        CMP BX,CX       ;COMPARE I AND COUNT
        JL NEXTPRIME    ;IF I<COUNT GOTO REPEAT

        ;PRINT THE PRIME SERIES
        prints MSG2
        MOV BX,00       ;BX=INDEX
        MOV SI,OFFSET RESULT    ;SI = STORAGE FOR ASCII STRING

NEXTPRN:
	lea bx,prime
	mov ax,[bx]
	printi ax
        prints NEWLINE
        prints RESULT              ;DISPLAY PRIME
        ADD BX,02                   ;ADJUST BX
        LOOP NEXTPRN                    ;REPEAT FOR ALL THE TERMS

	exit
;FUNCTION TO CONVERT HEXA DECIMAL NUMBER TO ASCII STRING
;AX - INPUT NUMBER
;SI - POINTER TO RESULT STORAGE AREA

HEX2ASC PROC   NEAR
        PUSH AX         ;SAVE REGISTER
        PUSH BX
        PUSH CX
        PUSH DX
        PUSH SI
        MOV CX,00H      ;COUNTER FOR INTERMEDIATE DATA PUSHED
        MOV BX,0AH      ;LOAD 10 IN BL

RPT1:
        MOV DX,00
        DIV BX          ;DIVIDED NUM BY 10
        ADD DL,'0'      ;CONVERT REMINDER TO ASCII
        PUSH DX         ;STORE ASCII DIGIT ON TO THE STACK
        INC CX          ;UPDATE COUNTER
        CMP AX,0AH      ;IS NUM LESS THAN OR EQUAL TO 10
        JGE RPT1        ;IF YES, PERFORM CONVERSION
        ADD AL,'0'      ;CONVERT LAST DIGIT TO ASCII
        MOV [SI],AL     ;STORE LAST DIGIT

        ;POP ALL INTERMEDIATE DATA FROM STACK AND STORE RESULT

RPT2:
        POP AX          ;POP DATA
        INC SI          ;ADVANCE RESULT STRING POINTER
        MOV [SI],AL     ;STORE IN RESULT
        LOOP RPT2
        INC SI
        MOV AL,'$'
        MOV [SI],AL     ;APPEND END OF STRING
        POP SI          ;RESTORE THE REGISTERS
        POP DX
        POP CX
        POP BX
        POP AX
        RET

HEX2ASC ENDP

CODE ENDS     
        END PRIMES