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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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