2.9BSD/usr/src/lib/ape/mult.c

#include "lint.h"
#ifndef lint
static char	sccs_id[] = "@(#)mult.c	2.1	7/6/82";
#endif lint
#include <ape.h>
struct half
{	short high;
	short low;
};
mult(a,b,c)  /* c = a * b */
MINT *a,*b,*c;
{	MINT x,y,z;
	int sign;

	sign = 1;
	x.val=a->val;
	y.val=b->val;
	z.len=0;
	if(a->len<0)
	{	x.len= -a->len;
		sign= -sign;
	}
	else	x.len=a->len;
	if(b->len<0)
	{	y.len= -b->len;
		sign= -sign;
	}
	else	y.len=b->len;
	if(x.len<y.len) m_mult(&y,&x,&z);
	else m_mult(&x,&y,&z);
	xfree(c);
	if (sign<0)
		c->len= -z.len;
	else
		c->len=z.len;
	c->val = z.val;
	if (c->len==0)
		shfree(c->val);
	return;
}
#define S2 x=a->val[j];
#define S3 x=x*b->val[i-j];
#define S4 tradd(&carry,&sum,x);
#define S5 c->val[i]=sum.yy.low&TOPSHORT;
#define S6 sum.xx=sum.xx>>15;
#define S7 sum.yy.high=carry;
m_mult(a,b,c) /* c = a * b for 0 <= a <= b */
MINT *a,*b,*c;
{	long x;
	union {long xx; struct half yy;} sum;
	int carry;
	int i,j;

	c->val=xalloc(a->len+b->len,"m_mult");
	sum.xx=0;
	for(i=0;i<b->len;i++)
	{	carry=0;
		for(j=0;j<i+1;j++)
		{	S2
			S3
			S4
		}
		S5
		S6
		S7
	}
	for(;i<a->len;i++)
	{	carry=0;
		for(j=i-b->len+1;j<i+1;j++)
		{	S2
			S3
			S4
		}
		S5
		S6
		S7
	}
	for(;i<a->len+b->len;i++)
	{	carry=0;
		for(j=i-b->len+1;j<a->len;j++)
		{	S2
			S3
			S4
		}
		S5
		S6
		S7
	}
	if(c->val[i-1]!=0)
		c->len=a->len+b->len;
	else	c->len=a->len+b->len-1;
	return;
}

tradd(a,b,c)
long c; int *a; union g {long xx; struct half yy;} *b;
{
	b->xx= b->xx+c;
	if(b->yy.high&CARRYBIT)
	{	b->yy.high= b->yy.high&TOPSHORT;
		*a += 1;
	}
	return;
}