mul_cal.c

C51库只提供长整形乘法

#include <intrins.h>
#include <string.h>
#include <absacc.h>
#include "reg52.h"

#define uchar	unsigned char
#define uint	unsigned int
#define ulong	unsigned long

/*--------------------------------------------------------------
	超长乘法(4字节*4字节==6字节)(高位在前,低位在后)
	入口参数:
		tmp1 == 被乘
		tmp2 == 乘
		buf == 积
	出口参数:
		== tmp1*tmp2/tmp3
--------------------------------------------------------------*/
void omul(ulong tmp1,ulong tmp2,uchar *buf)
{
	uint a,b,c,d,ii;
	ulong bd,ad,bc,ac,ee,ff;

	//tmp1*tmp2
	a = tmp1/0x10000;//取高位
	b = tmp1&0xffff;//取低位
	c = tmp2/0x10000;//取高位
	d = tmp2&0xffff;//取低位
	bd = (ulong)b*d;
	ad = (ulong)a*d;
	bc = (ulong)b*c;
	ac = (ulong)a*c;
	//乘积的低位
	ff = (ad&0xffff)+(bd/0x10000)+(bc&0xffff);
	ii = ff/0x10000;
	ff = ff*0x10000 + (bd&0xffff);
	//乘积的高位
	ee = (ac&0xffff0000) + ((ad/0x10000) + (ac&0xffff) + (bc/0x10000) + ii);
	//buf[7]=*((uchar *)(&ee)+3);
	//buf[6]=*((uchar *)(&ee)+2);
	buf[1]=*((uchar *)(&ee)+3);
	buf[0]=*((uchar *)(&ee)+2);

	buf[5]=*((uchar *)(&ff)+3);
	buf[4]=*((uchar *)(&ff)+2);
	buf[3]=*((uchar *)(&ff)+1);
	buf[2]=*(uchar *)(&ff);

}