116 lines
2.3 KiB
C
116 lines
2.3 KiB
C
#include <tommath.h>
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#ifdef BN_MP_DIV_D_C
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/* LibTomMath, multiple-precision integer library -- Tom St Denis
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*
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* LibTomMath is a library that provides multiple-precision
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* integer arithmetic as well as number theoretic functionality.
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*
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* The library was 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@gmail.com, http://libtom.org
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*/
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static int s_is_power_of_two(mp_digit b, int *p)
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{
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int x;
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/* fast return if no power of two */
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if ((b==0) || (b & (b-1))) {
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return 0;
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}
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for (x = 0; x < DIGIT_BIT; x++) {
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if (b == (((mp_digit)1)<<x)) {
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*p = x;
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return 1;
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}
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}
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return 0;
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}
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/* single digit division (based on routine from MPI) */
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int mp_div_d (mp_int * a, mp_digit b, mp_int * c, mp_digit * d)
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{
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mp_int q;
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mp_word w;
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mp_digit t;
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int res, ix;
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/* cannot divide by zero */
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if (b == 0) {
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return MP_VAL;
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}
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/* quick outs */
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if (b == 1 || mp_iszero(a) == 1) {
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if (d != NULL) {
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*d = 0;
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}
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if (c != NULL) {
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return mp_copy(a, c);
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}
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return MP_OKAY;
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}
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/* power of two ? */
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if (s_is_power_of_two(b, &ix) == 1) {
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if (d != NULL) {
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*d = a->dp[0] & ((((mp_digit)1)<<ix) - 1);
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}
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if (c != NULL) {
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return mp_div_2d(a, ix, c, NULL);
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}
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return MP_OKAY;
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}
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#ifdef BN_MP_DIV_3_C
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/* three? */
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if (b == 3) {
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return mp_div_3(a, c, d);
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}
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#endif
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/* no easy answer [c'est la vie]. Just division */
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if ((res = mp_init_size(&q, a->used)) != MP_OKAY) {
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return res;
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}
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q.used = a->used;
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q.sign = a->sign;
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w = 0;
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for (ix = a->used - 1; ix >= 0; ix--) {
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w = (w << ((mp_word)DIGIT_BIT)) | ((mp_word)a->dp[ix]);
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if (w >= b) {
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t = (mp_digit)(w / b);
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w -= ((mp_word)t) * ((mp_word)b);
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} else {
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t = 0;
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}
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q.dp[ix] = (mp_digit)t;
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}
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if (d != NULL) {
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*d = (mp_digit)w;
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}
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if (c != NULL) {
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mp_clamp(&q);
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mp_exch(&q, c);
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}
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mp_clear(&q);
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return res;
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}
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#endif
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/* $Source: /cvs/libtom/libtommath/bn_mp_div_d.c,v $ */
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/* $Revision: 1.5 $ */
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/* $Date: 2007/01/09 04:44:32 $ */
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