tmpright.c - plan9port - [fork] Plan 9 from user space
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       ---
       tmpright.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 }