1 #include "os.h" 2 #include <mp.h> 3 #include "dat.h" 4 5 // res = b >> shift 6 void 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