1 #include "os.h"
2 #include <mp.h>
3 #include "dat.h"
4 
5 /* res = b << shift */
6 void
7 mpleft(mpint *b, int shift, mpint *res)
8 {
9 	int d, l, r, i, otop;
10 	mpdigit this, last;
11 
12 	res->sign = b->sign;
13 	if(b->top==0){
14 		res->top = 0;
15 		return;
16 	}
17 
18 	/* a negative left shift is a right shift */
19 	if(shift < 0){
20 		mpright(b, -shift, res);
21 		return;
22 	}
23 
24 	/* b and res may be the same so remember the old top */
25 	otop = b->top;
26 
27 	/* shift */
28 	mpbits(res, otop*Dbits + shift);	/* overkill */
29 	res->top = DIGITS(otop*Dbits + shift);
30 	d = shift/Dbits;
31 	l = shift - d*Dbits;
32 	r = Dbits - l;
33 
34 	if(l == 0){
35 		for(i = otop-1; i >= 0; i--)
36 			res->p[i+d] = b->p[i];
37 	} else {
38 		last = 0;
39 		for(i = otop-1; i >= 0; i--) {
40 			this = b->p[i];
41 			res->p[i+d+1] = (last<<l) | (this>>r);
42 			last = this;
43 		}
44 		res->p[d] = last<<l;
45 	}
46 	for(i = 0; i < d; i++)
47 		res->p[i] = 0;
48 
49 	/* normalize */
50 	while(res->top > 0 && res->p[res->top-1] == 0)
51 		res->top--;
52 }