44 lines
842 B
C
44 lines
842 B
C
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#include "tommath_private.h"
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#ifdef MP_EXPT_N_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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/* calculate c = a**b using a square-multiply algorithm */
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mp_err mp_expt_n(const mp_int *a, int b, mp_int *c)
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{
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mp_err err;
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mp_int g;
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if ((err = mp_init_copy(&g, a)) != MP_OKAY) {
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return err;
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}
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/* set initial result */
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mp_set(c, 1uL);
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while (b > 0) {
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/* if the bit is set multiply */
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if ((b & 1) != 0) {
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if ((err = mp_mul(c, &g, c)) != MP_OKAY) {
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goto LBL_ERR;
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}
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}
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/* square */
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if (b > 1) {
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if ((err = mp_sqr(&g, &g)) != MP_OKAY) {
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goto LBL_ERR;
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}
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}
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/* shift to next bit */
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b >>= 1;
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}
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LBL_ERR:
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mp_clear(&g);
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return err;
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}
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#endif
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