45 lines
1023 B
C
45 lines
1023 B
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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/* b = a*2 */
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int
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mp_mul_2 (mp_int * a, mp_int * b)
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{
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mp_digit r, rr;
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int x, res;
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/* copy */
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if ((res = mp_copy (a, b)) != MP_OKAY) {
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return res;
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}
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if ((res = mp_grow (b, b->used + 1)) != MP_OKAY) {
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return res;
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}
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++b->used;
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/* shift any bit count < DIGIT_BIT */
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r = 0;
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for (x = 0; x < b->used; x++) {
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rr = (b->dp[x] >> (DIGIT_BIT - 1)) & 1;
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b->dp[x] = ((b->dp[x] << 1) | r) & MP_MASK;
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r = rr;
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}
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mp_clamp (b);
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return MP_OKAY;
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}
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