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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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// prereq: a >= b, alen >= blen, diff has at least alen digits
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void
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mpvecsub(mpdigit *a, int alen, mpdigit *b, int blen, mpdigit *diff)
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{
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	int i, borrow;
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	mpdigit x, y;
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	borrow = 0;
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	for(i = 0; i < blen; i++){
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		x = *a++;
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		y = *b++;
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		y += borrow;
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		if(y < borrow)
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			borrow = 1;
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		else
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			borrow = 0;
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		if(x < y)
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			borrow++;
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		*diff++ = x - y;
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	}
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	for(; i < alen; i++){
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		x = *a++;
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		y = x - borrow;
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		if(y > x)
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			borrow = 1;
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		else
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			borrow = 0;
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		*diff++ = y;
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	}
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}