22 lines
394 B
C
22 lines
394 B
C
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#include "os.h"
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#include <mp.h>
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#define iseven(a) (((a)->p[0] & 1) == 0)
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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 *dc1, *dc2; // don't care
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dc1 = mpnew(0);
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dc2 = mpnew(0);
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mpextendedgcd(b, m, dc1, res, dc2);
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if(mpcmp(dc1, mpone) != 0)
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abort();
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mpmod(res, m, res);
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mpfree(dc1);
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mpfree(dc2);
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}
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