114 lines
1.8 KiB
C
114 lines
1.8 KiB
C
/*
|
|
* Copyright (c) 1980 Regents of the University of California.
|
|
* All rights reserved. The Berkeley software License Agreement
|
|
* specifies the terms and conditions for redistribution.
|
|
*/
|
|
|
|
#ifndef lint
|
|
static char sccsid[] = "@(#)mult.c 1.1 94/10/31 SMI"; /* from UCB 5.1 4/30/85 */
|
|
#endif
|
|
|
|
/* LINTLIBRARY */
|
|
|
|
#include <mp.h>
|
|
|
|
mult(a,b,c)
|
|
register struct mint *a,*b,*c;
|
|
{
|
|
struct mint x,y;
|
|
int sign;
|
|
|
|
_mp_mcan(a);
|
|
_mp_mcan(b);
|
|
if (a->len == 0 || b->len == 0) {
|
|
xfree(c);
|
|
return;
|
|
}
|
|
sign = 1;
|
|
x.len = y.len = 0;
|
|
_mp_move(a, &x);
|
|
_mp_move(b, &y);
|
|
if (a->len < 0) {
|
|
x.len = -x.len;
|
|
sign = -sign;
|
|
}
|
|
if (b->len < 0) {
|
|
y.len = -y.len;
|
|
sign = -sign;
|
|
}
|
|
xfree(c);
|
|
if (x.len < y.len) {
|
|
m_mult(&x,&y,c);
|
|
} else {
|
|
m_mult(&y,&x,c);
|
|
}
|
|
if (sign < 0)
|
|
c->len = -c->len;
|
|
if (c->len == 0)
|
|
xfree(c);
|
|
xfree(&x);
|
|
xfree(&y);
|
|
}
|
|
|
|
/*
|
|
* Knuth 4.3.1, Algorithm M
|
|
*/
|
|
m_mult(a,b,c)
|
|
struct mint *a;
|
|
struct mint *b;
|
|
struct mint *c;
|
|
{
|
|
register int i,j;
|
|
register long sum;
|
|
register short bcache;
|
|
register short *aptr;
|
|
register short *bptr;
|
|
register short *cptr;
|
|
register unsigned short fifteen = 15;
|
|
register int alen;
|
|
int blen;
|
|
|
|
# define BASEBITS (8*sizeof(short)-1)
|
|
# define BASE (1 << BASEBITS)
|
|
# define LOWBITS (BASE - 1)
|
|
|
|
alen = a->len;
|
|
blen = b->len;
|
|
|
|
c->len = alen + blen;
|
|
c->val = xalloc(c->len,"m_mult");
|
|
|
|
aptr = a->val;
|
|
bptr = b->val;
|
|
cptr = c->val;
|
|
|
|
sum = 0;
|
|
bcache = *bptr++;
|
|
for (i = alen; i > 0; i--) {
|
|
sum += *aptr++ * bcache;
|
|
*cptr++ = sum & LOWBITS;
|
|
sum >>= fifteen;
|
|
}
|
|
*cptr = sum;
|
|
aptr -= alen;
|
|
cptr -= alen;
|
|
cptr++;
|
|
|
|
for (j = blen - 1; j > 0; j--) {
|
|
sum = 0;
|
|
bcache = *bptr++;
|
|
for (i = alen; i > 0; i--) {
|
|
sum += *aptr++ * bcache + *cptr;
|
|
*cptr++ = sum & LOWBITS;
|
|
sum >>= fifteen;
|
|
}
|
|
*cptr = sum;
|
|
aptr -= alen;
|
|
cptr -= alen;
|
|
cptr++;
|
|
}
|
|
if (c->val[c->len-1] == 0) {
|
|
c->len--;
|
|
}
|
|
}
|