mult_1.c

简易示波器 (采样点在屏上显示虚线曲线）

long mult_1(long a,char b)
{
	long result=0 ;
	unsigned char flag=0 ;	
	unsigned long a_32 ;
	unsigned char b_16 ;
	if(a<0)
	{
		a_32=-a ;
		flag ++ ;
	}
	else a_32 = a ;
	if(b<0)
	{
		b_16=-b ;
		flag ++ ;
	}
	else b_16 = b ;

//	result = a_32*b_16 ;

	if(b_16&0x0001==0x0001)result = result + a_32 ;
	if(b_16&0x0002==0x0002)result = result + (a_32<<1) ;
	if(b_16&0x0004==0x0004)result = result + (a_32<<2) ;
	if(b_16&0x0008==0x0008)result = result + (a_32<<3) ;
	if(b_16&0x0010==0x0010)result = result + (a_32<<4) ;
	if(b_16&0x0020==0x0020)result = result + (a_32<<5) ;
	if(b_16&0x0040==0x0040)result = result + (a_32<<6) ;

	if(flag==1)result = -result ;
	return result ;
}