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- #include "os.h"
- #include <mp.h>
- #include "dat.h"
- // res = b << shift
- void
- mpleft(mpint *b, int shift, mpint *res)
- {
- int d, l, r, i, otop;
- mpdigit this, last;
- res->sign = b->sign;
- if(b->top==0){
- res->top = 0;
- return;
- }
- // a negative left shift is a right shift
- if(shift < 0){
- mpright(b, -shift, res);
- return;
- }
- // b and res may be the same so remember the old top
- otop = b->top;
- // shift
- mpbits(res, otop*Dbits + shift); // overkill
- res->top = DIGITS(otop*Dbits + shift);
- d = shift/Dbits;
- l = shift - d*Dbits;
- r = Dbits - l;
- if(l == 0){
- for(i = otop-1; i >= 0; i--)
- res->p[i+d] = b->p[i];
- } else {
- last = 0;
- for(i = otop-1; i >= 0; i--) {
- this = b->p[i];
- res->p[i+d+1] = (last<<l) | (this>>r);
- last = this;
- }
- res->p[d] = last<<l;
- }
- for(i = 0; i < d; i++)
- res->p[i] = 0;
- // normalize
- while(res->top > 0 && res->p[res->top-1] == 0)
- res->top--;
- }
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