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28 lines
610 B
28 lines
610 B
#include "tommath_private.h"
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#ifdef BN_MP_DR_IS_MODULUS_C
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/* LibTomMath, multiple-precision integer library -- Tom St Denis */
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/* SPDX-License-Identifier: Unlicense */
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/* determines if a number is a valid DR modulus */
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mp_bool mp_dr_is_modulus(const mp_int *a)
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{
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int ix;
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/* must be at least two digits */
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if (a->used < 2) {
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return MP_NO;
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}
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/* must be of the form b**k - a [a <= b] so all
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* but the first digit must be equal to -1 (mod b).
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*/
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for (ix = 1; ix < a->used; ix++) {
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if (a->dp[ix] != MP_MASK) {
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return MP_NO;
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}
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}
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return MP_YES;
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}
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#endif
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