Detect 32-bit processor

det386.asm

format MZ
entry main:start
use16

segment main

start:
	call detect_i386
	mov dx, strings.error
	jnc .print
	mov dx, strings.ok
.print:
	mov ax, strings
	mov ds, ax
	mov ah, 0x09
	int 0x21
	mov ax, 0x4c00
	int 0x21

detect_i386:
	pushf       ; save FLAGS
	; clear FLAGS register
	xor cx, cx
	push cx
	popf
	pushf
	pop cx
	; test if top 2 bits (NT, reserved) are set
	test cx, 0xc000
	jnz .false
	; set NT and IOPL flags
	mov cx, 0x7000
	push cx
	popf
	pushf
	pop cx
	; test if NT and IOPL are still set
	test ch, 0x70
	jz .false
	popf
	stc
	ret
.false:
	popf
	clc
	ret

segment strings
.ok:
	db "OK!$"
.error:
	db "This program requires a i386-class or newer 32-bit processor.$"