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 // a negative right shift is a left shift
13 if(shift < 0){
14 mpleft(b, -shift, res);
15 return;
16 }
17
18 if(res != b)
19 mpbits(res, b->top*Dbits - shift);
20 d = shift/Dbits;
21 r = shift - d*Dbits;
22 l = Dbits - r;
23
24 // special case digit shifts
25 if(r == 0){
26 for(i = 0; i < b->top-d; i++)
27 res->p[i] = b->p[i+d];
28 } else {
29 last = b->p[d];
30 for(i = 0; i < b->top-d-1; i++){
31 this = b->p[i+d+1];
32 res->p[i] = (this<<l) | (last>>r);
33 last = this;
34 }
35 res->p[i++] = last>>r;
36 }
37 while(i > 0 && res->p[i-1] == 0)
38 i--;
39 res->top = i;
40 }
41