multiply.cpp

高效的乘法函数,不用调用系统乘法器,对没有乘法器的系统来说非常有用.

#include <iostream.h>
#include <stdio.h>
#include <math.h>
#include <conio.h>   
#include <stdlib.h>  

 
unsigned long multiply(unsigned short xp1, unsigned short xp2)
{
	unsigned long x[16];
	unsigned long sumx;
	unsigned int i;

	sumx = 0;
	for(i=0;i<16;i++){
		x[i]=(unsigned long)xp1;
	}
	for(i=0;i<16;i++){
		if(xp2&((unsigned short)1<<(15-i))){
			xp2-=(unsigned short)1<<(15-i);
			x[15-i]<<=(15-i);
		}
		else{
			x[15-i]=0;
		}
	}
	for(i=0;i<16;i++){
		sumx+=x[i];
	}
	return sumx;
}

unsigned long Mul(unsigned int x1, unsigned int x2)
{
	unsigned long sum;
	unsigned short p1,p2;

	if(x1>65535||x2>65535||x1<0||x2<0){
		cout<<"ERRO: Input out of scope!"<<endl;
		exit( 1 );
	}

	p1=(unsigned short)x1;
	p2=(unsigned short)x2;

	if(0==p1||0==p2){
		return 0;
	}
	if(p1>p2){
		sum=multiply(p1,p2);
	}
	else{
		sum=multiply(p2,p1);
	}
	return sum;
}	



int main(int argc, char *argv[])
{
	unsigned int x1, x2;

	cout<<"Arguements number:"<<argc<<"(Including the name of the application function)"<<endl;
	cout<<"Arguements are bellow:"<<endl;
	for(int index=0;index<argc;index++){
		cout<<argv[index]<<endl;
	}
	for(;;){
		cout<<"Input x1 and x2 (0~65535)"<<endl;

		scanf("%ld",&x1);
		scanf("%ld",&x2);

		cout<<"result is:"<<Mul(x1,x2)<<endl;
	}

	return 0;
}