mpright.c (884B)
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 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 }