## File: bn_mp_montgomery_calc_normalization.c

package info (click to toggle)
libtommath 1.1.0-3
 `1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556` ``````#include "tommath_private.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. * * SPDX-License-Identifier: Unlicense */ /* * 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, const 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, 1uL); 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 /* ref: HEAD -> master, tag: v1.1.0 */ /* git commit: 08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */ /* commit time: 2019-01-28 20:32:32 +0100 */ ``````