//-------------------------------------------------------------------
//	useasm.cpp
//
//	This program illustrates the use of GCC's 'asm' construct to
//	insert inline assembly language statements into your program 
//	(in cases where you need to reference your local variables).
//
//	   	asm( instruction-template 
//	   		: output-operand
//	   		: input-operand
//	   		: clobber-list );
//
//	To see the assembly-language generated by the asm construct,
//	you can use this command-sequence:  
//
//			$ gcc -S useasm.cpp
//			$ cat useasm.s
//				   
//	programmer: ALLAN CRUSE
//	written on: 18 OCT 2004
//-------------------------------------------------------------------

#include <stdio.h>	// for printf(), perror() 
#include <fcntl.h>	// for open() 
#include <stdlib.h>	// for exit() 
#include <unistd.h>	// for read(), write(), close() 

int	c = 10;		// static variable (global)

int main( int argc, char **argv )
{
	int	x = 25;	// automatic variable (local)
	int	y;	// automatic variable (local) 

	// using several single-instruction constructs
	asm("	movl	%0, %%eax " : : "m" (x) );
	asm("	mull	c " : : : "edx" );
	asm("	shl	$1, %eax ");
	asm("	movl	%%eax, %0 " : "=m" (y) );
	printf( "x=%d  y=%d  \n", x, y );

	// using just one multi-instruction construct
	asm("	movl	%1, %%eax 	\n	\
		mull	c 		\n	\
		shl	$1, %%eax	\n	\
		movl	%%eax, %0 "
			: "=m" (y) : "m" (x) : "edx" ); 		
	printf( "x=%d  y=%d  \n", x, y );
}