mirror of
https://github.com/clearml/dropbear
synced 2025-01-31 02:46:58 +00:00
8608a8e64c
to branch 'au.asn.ucc.matt.dropbear' (head fff0894a0399405a9410ea1c6d118f342cf2aa64) --HG-- extra : convert_revision : fdf4a7a3b97ae5046139915de7e40399cceb2c01
56 lines
1.4 KiB
C
56 lines
1.4 KiB
C
#include <tommath.h>
|
|
#ifdef BN_MP_MONTGOMERY_CALC_NORMALIZATION_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
|
|
* additional optimizations in place.
|
|
*
|
|
* The library is free for all purposes without any express
|
|
* guarantee it works.
|
|
*
|
|
* Tom St Denis, tomstdenis@iahu.ca, http://math.libtomcrypt.org
|
|
*/
|
|
|
|
/*
|
|
* shifts with subtractions when the result is greater than b.
|
|
*
|
|
* The method is slightly modified to shift B unconditionally upto just under
|
|
* the leading bit of b. This saves alot of multiple precision shifting.
|
|
*/
|
|
int mp_montgomery_calc_normalization (mp_int * a, mp_int * b)
|
|
{
|
|
int x, bits, res;
|
|
|
|
/* how many bits of last digit does b use */
|
|
bits = mp_count_bits (b) % DIGIT_BIT;
|
|
|
|
if (b->used > 1) {
|
|
if ((res = mp_2expt (a, (b->used - 1) * DIGIT_BIT + bits - 1)) != MP_OKAY) {
|
|
return res;
|
|
}
|
|
} else {
|
|
mp_set(a, 1);
|
|
bits = 1;
|
|
}
|
|
|
|
|
|
/* now compute C = A * B mod b */
|
|
for (x = bits - 1; x < (int)DIGIT_BIT; x++) {
|
|
if ((res = mp_mul_2 (a, a)) != MP_OKAY) {
|
|
return res;
|
|
}
|
|
if (mp_cmp_mag (a, b) != MP_LT) {
|
|
if ((res = s_mp_sub (a, b, a)) != MP_OKAY) {
|
|
return res;
|
|
}
|
|
}
|
|
}
|
|
|
|
return MP_OKAY;
|
|
}
|
|
#endif
|