238 lines
6.3 KiB
NASM
238 lines
6.3 KiB
NASM
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; 8086 assembly to compute e to n digits.
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; build with masm 5.0 like this:
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; ntvdm -h masm /Zi /Zd /z /l %1,,,;
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; ntvdm -h link %1,,%1,,nul.def
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; replicate this:
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; #define TRUE 1
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; #define FALSE 0
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; #define SIZE 8190
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;
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; char flags[SIZE+1];
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;
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; int main()
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; {
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; int i,k;
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; int prime,count,iter;
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;
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; for (iter = 1; iter <= 10; iter++) { /* do program 10 times */
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; count = 0; /* initialize prime counter */
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; for (i = 0; i <= SIZE; i++) /* set all flags true */
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; flags[i] = TRUE;
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; for (i = 0; i <= SIZE; i++) {
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; if (flags[i]) { /* found a prime */
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; prime = i + i + 3; /* twice index + 3 */
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; for (k = i + prime; k <= SIZE; k += prime)
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; flags[k] = FALSE; /* kill all multiples */
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; count++; /* primes found */
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; }
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; }
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; }
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; printf("%d primes.\n",count); /*primes found in 10th pass */
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; return 0;
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; }
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;
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dosseg
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.model small
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.stack 100h
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; DOS constants
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dos_write_char equ 2h
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dos_realtime_clock equ 1ah
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dos_exit equ 4ch
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; app constants
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true equ 1
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false equ 0
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loops equ 10
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arraysize equ 8190
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dataseg segment para public 'data'
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assume ds: dataseg
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crlfmsg db 13,10,0
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primesmsg db ' primes.',13,10,0
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count dw 0
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ITER dw 0
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PKFLAGS dd 0
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align 16
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flags db arraysize + 1 dup( ? )
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afterflags db 0
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dataseg ends
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.code
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start:
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mov ax, dataseg
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mov ds, ax
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mov cx, 0 ; handy place for 0
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mov di, offset afterFlags ; handy place for this constant
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iteragain: ; for ( iter = 1; iter <= 10; iter++ )
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mov word ptr [ count ], 0 ; count = 0
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; set all array entries to true: for (i = 0; i <= SIZE; i++) flags[i] = TRUE;
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xor bx, bx
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nexttrue:
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mov byte ptr [ offset flags + bx ], true
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inc bx
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cmp bx, arraysize
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jle nexttrue
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; iterate through array entries and count primes
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xor bx, bx ; bx is "i" in the outer for loop
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nextprime: ; for (i = 0; i <= SIZE; i++) {
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cmp byte ptr [ flags + bx ], 0
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jz flagisoff
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mov ax, 3 ; ax == prime = i + i + 3
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add ax, bx
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add ax, bx
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mov si, offset flags
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add si, bx ; for (k = i + prime; k <= SIZE; k += prime)
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kloop:
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add si, ax ; k += prime
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cmp si, di ; is si >= offset afterFlags?
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jge inccount
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mov byte ptr [ si ], cl ; flags[ k ] = false. use cl for 0 because it's faster than an immediate
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jmp kloop
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inccount:
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inc word ptr [ COUNT ] ; count++
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flagisoff: ; check if outer loop is done
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inc bx
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cmp bx, arraysize + 1
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jnz nextprime
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checknextiter: ; are we done iterating loops times?
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inc word ptr [ ITER ]
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cmp word ptr [ ITER ], loops
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jnz iteragain
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mov ax, word ptr [COUNT]
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call printint
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call printcrlf
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mov dx, offset primesmsg
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call printstring
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mov al, 0
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mov ah, dos_exit
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int 21h
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;start endp
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; print the integer in ax
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printint proc near
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test ah, 80h
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push ax
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push bx
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push cx
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push dx
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push di
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push si
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jz _prpositive
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neg ax ; just one instruction for complement + 1
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push ax
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mov dx, '-'
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mov ah, dos_write_char
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int 21h
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pop ax
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_prpositive:
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xor cx, cx
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xor dx, dx
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cmp ax, 0
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je _przero
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_prlabel1:
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cmp ax, 0
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je _prprint1
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mov bx, 10
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div bx
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push dx
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inc cx
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xor dx, dx
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jmp _prlabel1
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_prprint1:
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cmp cx, 0
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je _prexit
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pop dx
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add dx, 48
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mov ah, dos_write_char
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int 21h
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dec cx
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jmp _prprint1
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_przero:
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mov dx, '0'
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mov ah, dos_write_char
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int 21h
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_prexit:
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pop si
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pop di
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pop dx
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pop cx
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pop bx
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pop ax
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ret
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printint endp
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printcrlf proc near
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push ax
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push bx
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push cx
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push dx
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push di
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push si
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mov dx, offset crlfmsg
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call printstring
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pop si
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pop di
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pop dx
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pop cx
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pop bx
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pop ax
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ret
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printcrlf endp
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printstring proc near
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push ax
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push bx
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push cx
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push dx
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push di
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push si
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mov di, dx
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_psnext:
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mov al, byte ptr [ di ]
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cmp al, 0
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je _psdone
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mov dx, ax
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mov ah, dos_write_char
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int 21h
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inc di
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jmp _psnext
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_psdone:
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pop si
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pop di
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pop dx
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pop cx
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pop bx
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pop ax
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ret
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printstring endp
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end
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