### view libtommath/bn_mp_reduce_2k.c @ 1470:8bba51a55704

Update to libtommath v1.0.1
author Matt Johnston Thu, 08 Feb 2018 23:11:40 +0800 60fc6476e044 f52919ffd3b1
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```#include <tommath_private.h>
#ifdef BN_MP_REDUCE_2K_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis
*
* LibTomMath is a library that provides multiple-precision
* integer arithmetic as well as number theoretic functionality.
*
* The library was designed directly after the MPI library by
* Michael Fromberger but has been written from scratch with
*
* The library is free for all purposes without any express
* guarantee it works.
*
* Tom St Denis, [email protected], http://libtom.org
*/

/* reduces a modulo n where n is of the form 2**p - d */
int mp_reduce_2k(mp_int *a, mp_int *n, mp_digit d)
{
mp_int q;
int    p, res;

if ((res = mp_init(&q)) != MP_OKAY) {
return res;
}

p = mp_count_bits(n);
top:
/* q = a/2**p, a = a mod 2**p */
if ((res = mp_div_2d(a, p, &q, a)) != MP_OKAY) {
goto ERR;
}

if (d != 1) {
/* q = q * d */
if ((res = mp_mul_d(&q, d, &q)) != MP_OKAY) {
goto ERR;
}
}

/* a = a + q */
if ((res = s_mp_add(a, &q, a)) != MP_OKAY) {
goto ERR;
}

if (mp_cmp_mag(a, n) != MP_LT) {
if ((res = s_mp_sub(a, n, a)) != MP_OKAY) {
goto ERR;
}
goto top;
}

ERR:
mp_clear(&q);
return res;
}

#endif

/* ref:         \$Format:%D\$ */
/* git commit:  \$Format:%H\$ */
/* commit time: \$Format:%ai\$ */
```