tmpleft.c - plan9port - [fork] Plan 9 from user space
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       ---
       tmpleft.c (924B)
       ---
            1 #include "os.h"
            2 #include <mp.h>
            3 #include "dat.h"
            4 
            5 /* res = b << shift */
            6 void
            7 mpleft(mpint *b, int shift, mpint *res)
            8 {
            9         int d, l, r, i, otop;
           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 left shift is a right shift */
           19         if(shift < 0){
           20                 mpright(b, -shift, res);
           21                 return;
           22         }
           23 
           24         /* b and res may be the same so remember the old top */
           25         otop = b->top;
           26 
           27         /* shift */
           28         mpbits(res, otop*Dbits + shift);        /* overkill */
           29         res->top = DIGITS(otop*Dbits + shift);
           30         d = shift/Dbits;
           31         l = shift - d*Dbits;
           32         r = Dbits - l;
           33 
           34         if(l == 0){
           35                 for(i = otop-1; i >= 0; i--)
           36                         res->p[i+d] = b->p[i];
           37         } else {
           38                 last = 0;
           39                 for(i = otop-1; i >= 0; i--) {
           40                         this = b->p[i];
           41                         res->p[i+d+1] = (last<<l) | (this>>r);
           42                         last = this;
           43                 }
           44                 res->p[d] = last<<l;
           45         }
           46         for(i = 0; i < d; i++)
           47                 res->p[i] = 0;
           48 
           49         /* normalize */
           50         while(res->top > 0 && res->p[res->top-1] == 0)
           51                 res->top--;
           52 }