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