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#include "os.h"
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#include <mp.h>
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// use extended gcd to find the multiplicative inverse
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// res = b**-1 mod m
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void
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mpinvert(mpint *b, mpint *m, mpint *res)
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{
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	mpint *v;
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	v = mpnew(0);
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	mpextendedgcd(b, m, v, res, nil);
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	if(mpcmp(v, mpone) != 0)
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		abort();
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	mpfree(v);
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	mpmod(res, m, res);
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}