diff options
Diffstat (limited to 'libtommath/bn_fast_mp_invmod.c')
| -rw-r--r-- | libtommath/bn_fast_mp_invmod.c | 160 |
1 files changed, 0 insertions, 160 deletions
diff --git a/libtommath/bn_fast_mp_invmod.c b/libtommath/bn_fast_mp_invmod.c deleted file mode 100644 index 9ce434f..0000000 --- a/libtommath/bn_fast_mp_invmod.c +++ /dev/null @@ -1,160 +0,0 @@ -#include "tommath_private.h" -#ifdef BN_FAST_MP_INVMOD_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 - */ - -/* computes the modular inverse via binary extended euclidean algorithm, - * that is c = 1/a mod b - * - * Based on slow invmod except this is optimized for the case where b is - * odd as per HAC Note 14.64 on pp. 610 - */ -int fast_mp_invmod(const mp_int *a, const mp_int *b, mp_int *c) -{ - mp_int x, y, u, v, B, D; - int res, neg; - - /* 2. [modified] b must be odd */ - if (mp_iseven(b) == MP_YES) { - return MP_VAL; - } - - /* init all our temps */ - if ((res = mp_init_multi(&x, &y, &u, &v, &B, &D, NULL)) != MP_OKAY) { - return res; - } - - /* x == modulus, y == value to invert */ - if ((res = mp_copy(b, &x)) != MP_OKAY) { - goto LBL_ERR; - } - - /* we need y = |a| */ - if ((res = mp_mod(a, b, &y)) != MP_OKAY) { - goto LBL_ERR; - } - - /* if one of x,y is zero return an error! */ - if ((mp_iszero(&x) == MP_YES) || (mp_iszero(&y) == MP_YES)) { - res = MP_VAL; - goto LBL_ERR; - } - - /* 3. u=x, v=y, A=1, B=0, C=0,D=1 */ - if ((res = mp_copy(&x, &u)) != MP_OKAY) { - goto LBL_ERR; - } - if ((res = mp_copy(&y, &v)) != MP_OKAY) { - goto LBL_ERR; - } - mp_set(&D, 1uL); - -top: - /* 4. while u is even do */ - while (mp_iseven(&u) == MP_YES) { - /* 4.1 u = u/2 */ - if ((res = mp_div_2(&u, &u)) != MP_OKAY) { - goto LBL_ERR; - } - /* 4.2 if B is odd then */ - if (mp_isodd(&B) == MP_YES) { - if ((res = mp_sub(&B, &x, &B)) != MP_OKAY) { - goto LBL_ERR; - } - } - /* B = B/2 */ - if ((res = mp_div_2(&B, &B)) != MP_OKAY) { - goto LBL_ERR; - } - } - - /* 5. while v is even do */ - while (mp_iseven(&v) == MP_YES) { - /* 5.1 v = v/2 */ - if ((res = mp_div_2(&v, &v)) != MP_OKAY) { - goto LBL_ERR; - } - /* 5.2 if D is odd then */ - if (mp_isodd(&D) == MP_YES) { - /* D = (D-x)/2 */ - if ((res = mp_sub(&D, &x, &D)) != MP_OKAY) { - goto LBL_ERR; - } - } - /* D = D/2 */ - if ((res = mp_div_2(&D, &D)) != MP_OKAY) { - goto LBL_ERR; - } - } - - /* 6. if u >= v then */ - if (mp_cmp(&u, &v) != MP_LT) { - /* u = u - v, B = B - D */ - if ((res = mp_sub(&u, &v, &u)) != MP_OKAY) { - goto LBL_ERR; - } - - if ((res = mp_sub(&B, &D, &B)) != MP_OKAY) { - goto LBL_ERR; - } - } else { - /* v - v - u, D = D - B */ - if ((res = mp_sub(&v, &u, &v)) != MP_OKAY) { - goto LBL_ERR; - } - - if ((res = mp_sub(&D, &B, &D)) != MP_OKAY) { - goto LBL_ERR; - } - } - - /* if not zero goto step 4 */ - if (mp_iszero(&u) == MP_NO) { - goto top; - } - - /* now a = C, b = D, gcd == g*v */ - - /* if v != 1 then there is no inverse */ - if (mp_cmp_d(&v, 1uL) != MP_EQ) { - res = MP_VAL; - goto LBL_ERR; - } - - /* b is now the inverse */ - neg = a->sign; - while (D.sign == MP_NEG) { - if ((res = mp_add(&D, b, &D)) != MP_OKAY) { - goto LBL_ERR; - } - } - - /* too big */ - while (mp_cmp_mag(&D, b) != MP_LT) { - if ((res = mp_sub(&D, b, &D)) != MP_OKAY) { - goto LBL_ERR; - } - } - - mp_exch(&D, c); - c->sign = neg; - res = MP_OKAY; - -LBL_ERR: - mp_clear_multi(&x, &y, &u, &v, &B, &D, NULL); - return res; -} -#endif - -/* ref: HEAD -> master, tag: v1.1.0 */ -/* git commit: 08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */ -/* commit time: 2019-01-28 20:32:32 +0100 */ |