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1 #include "os.h"2 #include <mp.h>3 #include "dat.h"5 // res = b >> shift6 void7 mpright(mpint *b, int shift, mpint *res)8 {9 int d, l, r, i;10 mpdigit this, last;12 res->sign = b->sign;13 if(b->top==0){14 res->top = 0;15 return;16 }18 // a negative right shift is a left shift19 if(shift < 0){20 mpleft(b, -shift, res);21 return;22 }24 if(res != b)25 mpbits(res, b->top*Dbits - shift);26 d = shift/Dbits;27 r = shift - d*Dbits;28 l = Dbits - r;30 // shift all the bits out == zero31 if(d>=b->top){32 res->top = 0;33 return;34 }36 // special case digit shifts37 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 }