30 lines
771 B
C
30 lines
771 B
C
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#include "tommath_private.h"
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#ifdef MP_INVMOD_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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/* hac 14.61, pp608 */
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mp_err mp_invmod(const mp_int *a, const mp_int *b, mp_int *c)
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{
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/* for all n in N and n > 0, n = 0 mod 1 */
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if (!mp_isneg(a) && mp_cmp_d(b, 1uL) == MP_EQ) {
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mp_zero(c);
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return MP_OKAY;
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}
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/* b cannot be negative and has to be >1 */
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if (mp_isneg(b) || (mp_cmp_d(b, 1uL) != MP_GT)) {
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return MP_VAL;
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}
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/* if the modulus is odd we can use a faster routine instead */
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if (MP_HAS(S_MP_INVMOD_ODD) && mp_isodd(b)) {
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return s_mp_invmod_odd(a, b, c);
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}
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return MP_HAS(S_MP_INVMOD)
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? s_mp_invmod(a, b, c)
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: MP_VAL;
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}
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#endif
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