54 lines
1.1 KiB
C
54 lines
1.1 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://libtommath.iahu.ca
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*/
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#include <tommath.h>
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/* setups the montgomery reduction stuff */
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int
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mp_montgomery_setup (mp_int * a, mp_digit * mp)
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{
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mp_int t, tt;
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int res;
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if ((res = mp_init (&t)) != MP_OKAY) {
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return res;
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}
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if ((res = mp_init (&tt)) != MP_OKAY) {
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goto __T;
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}
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/* tt = b */
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tt.dp[0] = 0;
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tt.dp[1] = 1;
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tt.used = 2;
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/* t = m mod b */
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t.dp[0] = a->dp[0];
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t.used = 1;
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/* t = 1/m mod b */
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if ((res = mp_invmod (&t, &tt, &t)) != MP_OKAY) {
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goto __TT;
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}
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/* t = -1/m mod b */
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*mp = ((mp_digit) 1 << ((mp_digit) DIGIT_BIT)) - t.dp[0];
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res = MP_OKAY;
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__TT:mp_clear (&tt);
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__T:mp_clear (&t);
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return res;
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}
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