1 #include "os.h"
2 #include <mp.h>
3 #include "dat.h"
4
5 // res = b << shift
6 void
mpleft(mpint * b,int shift,mpint * res)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 }
53