1 #include "os.h"
2 #include <mp.h>
3 #include "dat.h"
4
5 // res = b >> shift
6 void
mpright(mpint * b,int shift,mpint * res)7 mpright(mpint *b, int shift, mpint *res)
8 {
9 int d, l, r, i;
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 right shift is a left shift
19 if(shift < 0){
20 mpleft(b, -shift, res);
21 return;
22 }
23
24 if(res != b)
25 mpbits(res, b->top*Dbits - shift);
26 d = shift/Dbits;
27 r = shift - d*Dbits;
28 l = Dbits - r;
29
30 // shift all the bits out == zero
31 if(d>=b->top){
32 res->top = 0;
33 return;
34 }
35
36 // special case digit shifts
37 if(r == 0){
38 for(i = 0; i < b->top-d; i++)
39 res->p[i] = b->p[i+d];
40 } else {
41 last = b->p[d];
42 for(i = 0; i < b->top-d-1; i++){
43 this = b->p[i+d+1];
44 res->p[i] = (this<<l) | (last>>r);
45 last = this;
46 }
47 res->p[i++] = last>>r;
48 }
49 while(i > 0 && res->p[i-1] == 0)
50 i--;
51 res->top = i;
52 if(i==0)
53 res->sign = 1;
54 }
55