t8-mod/deps/libtommath/mp_div_2.c

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2024-02-15 15:46:47 -05:00
#include "tommath_private.h"
#ifdef MP_DIV_2_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */
/* b = a/2 */
mp_err mp_div_2(const mp_int *a, mp_int *b)
{
mp_err err;
int x, oldused;
mp_digit r;
if ((err = mp_grow(b, a->used)) != MP_OKAY) {
return err;
}
oldused = b->used;
b->used = a->used;
/* carry */
r = 0;
for (x = b->used; x --> 0;) {
/* get the carry for the next iteration */
mp_digit rr = a->dp[x] & 1u;
/* shift the current digit, add in carry and store */
b->dp[x] = (a->dp[x] >> 1) | (r << (MP_DIGIT_BIT - 1));
/* forward carry to next iteration */
r = rr;
}
/* zero excess digits */
s_mp_zero_digs(b->dp + b->used, oldused - b->used);
b->sign = a->sign;
mp_clamp(b);
return MP_OKAY;
}
#endif