libtommath/bn_mp_reduce_is_2k.c

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#include <tommath.h>
#ifdef BN_MP_REDUCE_IS_2K_C
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/* LibTomMath, multiple-precision integer library -- Tom St Denis
*
* LibTomMath is a library that provides multiple-precision
* integer arithmetic as well as number theoretic functionality.
*
* The library was designed directly after the MPI library by
* Michael Fromberger but has been written from scratch with
* additional optimizations in place.
*
* The library is free for all purposes without any express
* guarantee it works.
*
2007-04-18 09:58:18 +00:00
* Tom St Denis, tomstdenis@gmail.com, http://libtom.org
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*/
/* determines if mp_reduce_2k can be used */
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int mp_reduce_is_2k(mp_int *a)
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{
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int ix, iy, iw;
mp_digit iz;
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if (a->used == 0) {
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return MP_NO;
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} else if (a->used == 1) {
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return MP_YES;
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} else if (a->used > 1) {
iy = mp_count_bits(a);
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iz = 1;
iw = 1;
/* Test every bit from the second digit up, must be 1 */
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for (ix = DIGIT_BIT; ix < iy; ix++) {
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if ((a->dp[iw] & iz) == 0) {
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return MP_NO;
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}
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iz <<= 1;
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if (iz > (mp_digit)MP_MASK) {
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++iw;
iz = 1;
}
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}
}
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return MP_YES;
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}
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#endif
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/* $Source$ */
/* $Revision$ */
/* $Date$ */