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#include "tommath_private.h"
#ifdef BN_MP_MOD_2D_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */
/* calc a value mod 2**b */
mp_err mp_mod_2d(const mp_int *a, int b, mp_int *c)
{
int x;
mp_err err;
/* if b is <= 0 then zero the int */
if (b <= 0) {
mp_zero(c);
return MP_OKAY;
}
/* if the modulus is larger than the value than return */
if (b >= (a->used * MP_DIGIT_BIT)) {
return mp_copy(a, c);
}
/* copy */
if ((err = mp_copy(a, c)) != MP_OKAY) {
return err;
}
/* zero digits above the last digit of the modulus */
x = (b / MP_DIGIT_BIT) + (((b % MP_DIGIT_BIT) == 0) ? 0 : 1);
MP_ZERO_DIGITS(c->dp + x, c->used - x);
/* clear the digit that is not completely outside/inside the modulus */
c->dp[b / MP_DIGIT_BIT] &=
((mp_digit)1 << (mp_digit)(b % MP_DIGIT_BIT)) - (mp_digit)1;
mp_clamp(c);
return MP_OKAY;
}
#endif
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