79 lines
1.8 KiB
C
79 lines
1.8 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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/* shift right by a certain bit count (store quotient in c, remainder in d) */
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int
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mp_div_2d (mp_int * a, int b, mp_int * c, mp_int * d)
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{
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mp_digit D, r, rr;
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int x, res;
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mp_int t;
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/* if the shift count is <= 0 then we do no work */
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if (b <= 0) {
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res = mp_copy (a, c);
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if (d != NULL) {
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mp_zero (d);
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}
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return res;
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}
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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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/* get the remainder */
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if (d != NULL) {
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if ((res = mp_mod_2d (a, b, &t)) != MP_OKAY) {
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mp_clear (&t);
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return res;
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}
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}
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/* copy */
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if ((res = mp_copy (a, c)) != MP_OKAY) {
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mp_clear (&t);
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return res;
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}
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/* shift by as many digits in the bit count */
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mp_rshd (c, b / DIGIT_BIT);
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/* shift any bit count < DIGIT_BIT */
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D = (mp_digit) (b % DIGIT_BIT);
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if (D != 0) {
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r = 0;
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for (x = c->used - 1; x >= 0; x--) {
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/* get the lower bits of this word in a temp */
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rr = c->dp[x] & ((mp_digit) ((1U << D) - 1U));
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/* shift the current word and mix in the carry bits from the previous word */
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c->dp[x] = (c->dp[x] >> D) | (r << (DIGIT_BIT - D));
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/* set the carry to the carry bits of the current word found above */
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r = rr;
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}
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}
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mp_clamp (c);
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res = MP_OKAY;
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if (d != NULL) {
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mp_exch (&t, d);
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}
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mp_clear (&t);
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return MP_OKAY;
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}
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