39 lines
971 B
C
39 lines
971 B
C
#include "tommath_private.h"
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#ifdef BN_MP_MOD_2D_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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/* calc a value mod 2**b */
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mp_err mp_mod_2d(const mp_int *a, int b, mp_int *c)
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{
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int x;
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mp_err err;
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/* if b is <= 0 then zero the int */
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if (b <= 0) {
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mp_zero(c);
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return MP_OKAY;
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}
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/* if the modulus is larger than the value than return */
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if (b >= (a->used * MP_DIGIT_BIT)) {
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return mp_copy(a, c);
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}
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/* copy */
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if ((err = mp_copy(a, c)) != MP_OKAY) {
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return err;
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}
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/* zero digits above the last digit of the modulus */
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x = (b / MP_DIGIT_BIT) + (((b % MP_DIGIT_BIT) == 0) ? 0 : 1);
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MP_ZERO_DIGITS(c->dp + x, c->used - x);
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/* clear the digit that is not completely outside/inside the modulus */
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c->dp[b / MP_DIGIT_BIT] &=
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((mp_digit)1 << (mp_digit)(b % MP_DIGIT_BIT)) - (mp_digit)1;
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mp_clamp(c);
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return MP_OKAY;
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}
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#endif
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