43 lines
1.0 KiB
C
43 lines
1.0 KiB
C
/* LibTomMath, multiple-precision integer library -- Tom St Denis
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*
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* LibTomMath is library that provides for multiple-precision
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* integer arithmetic as well as number theoretic functionality.
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*
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* The library is designed directly after the MPI library by
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* Michael Fromberger but has been written from scratch with
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* additional optimizations in place.
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*
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* The library is free for all purposes without any express
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* guarantee it works.
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*
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* Tom St Denis, tomstdenis@iahu.ca, http://math.libtomcrypt.org
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*/
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#include <tommath.h>
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/* determines the setup value */
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int
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mp_reduce_2k_setup(mp_int *a, mp_digit *d)
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{
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int res, p;
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mp_int tmp;
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if ((res = mp_init(&tmp)) != MP_OKAY) {
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return res;
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}
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p = mp_count_bits(a);
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if ((res = mp_2expt(&tmp, p)) != MP_OKAY) {
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mp_clear(&tmp);
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return res;
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}
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if ((res = s_mp_sub(&tmp, a, &tmp)) != MP_OKAY) {
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mp_clear(&tmp);
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return res;
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}
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*d = tmp.dp[0];
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mp_clear(&tmp);
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return MP_OKAY;
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}
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