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simplifications: invmod

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This commit is contained in:
Daniel Mendler 2019-10-29 20:21:22 +01:00
parent 56144eed1e
commit b1f9bff192
No known key found for this signature in database
GPG Key ID: D88ADB2A2693CA43
2 changed files with 76 additions and 80 deletions
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70
s_mp_invmod_fast.c
View File

@ -42,51 +42,49 @@ mp_err s_mp_invmod_fast(const mp_int *a, const mp_int *b, mp_int *c)
if ((err = mp_copy(&y, &v)) != MP_OKAY) goto LBL_ERR;
mp_set(&D, 1uL);
top:
/* 4. while u is even do */
while (mp_iseven(&u)) {
/* 4.1 u = u/2 */
if ((err = mp_div_2(&u, &u)) != MP_OKAY) goto LBL_ERR;
do {
/* 4. while u is even do */
while (mp_iseven(&u)) {
/* 4.1 u = u/2 */
if ((err = mp_div_2(&u, &u)) != MP_OKAY) goto LBL_ERR;
/* 4.2 if B is odd then */
if (mp_isodd(&B)) {
if ((err = mp_sub(&B, &x, &B)) != MP_OKAY) goto LBL_ERR;
/* 4.2 if B is odd then */
if (mp_isodd(&B)) {
if ((err = mp_sub(&B, &x, &B)) != MP_OKAY) goto LBL_ERR;
}
/* B = B/2 */
if ((err = mp_div_2(&B, &B)) != MP_OKAY) goto LBL_ERR;
}
/* B = B/2 */
if ((err = mp_div_2(&B, &B)) != MP_OKAY) goto LBL_ERR;
}
/* 5. while v is even do */
while (mp_iseven(&v)) {
/* 5.1 v = v/2 */
if ((err = mp_div_2(&v, &v)) != MP_OKAY) goto LBL_ERR;
/* 5. while v is even do */
while (mp_iseven(&v)) {
/* 5.1 v = v/2 */
if ((err = mp_div_2(&v, &v)) != MP_OKAY) goto LBL_ERR;
/* 5.2 if D is odd then */
if (mp_isodd(&D)) {
/* D = (D-x)/2 */
if ((err = mp_sub(&D, &x, &D)) != MP_OKAY) goto LBL_ERR;
/* 5.2 if D is odd then */
if (mp_isodd(&D)) {
/* D = (D-x)/2 */
if ((err = mp_sub(&D, &x, &D)) != MP_OKAY) goto LBL_ERR;
}
/* D = D/2 */
if ((err = mp_div_2(&D, &D)) != MP_OKAY) goto LBL_ERR;
}
/* D = D/2 */
if ((err = 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 ((err = mp_sub(&u, &v, &u)) != MP_OKAY) goto LBL_ERR;
/* 6. if u >= v then */
if (mp_cmp(&u, &v) != MP_LT) {
/* u = u - v, B = B - D */
if ((err = mp_sub(&u, &v, &u)) != MP_OKAY) goto LBL_ERR;
if ((err = mp_sub(&B, &D, &B)) != MP_OKAY) goto LBL_ERR;
} else {
/* v - v - u, D = D - B */
if ((err = mp_sub(&v, &u, &v)) != MP_OKAY) goto LBL_ERR;
if ((err = mp_sub(&B, &D, &B)) != MP_OKAY) goto LBL_ERR;
} else {
/* v - v - u, D = D - B */
if ((err = mp_sub(&v, &u, &v)) != MP_OKAY) goto LBL_ERR;
if ((err = mp_sub(&D, &B, &D)) != MP_OKAY) goto LBL_ERR;
}
if ((err = mp_sub(&D, &B, &D)) != MP_OKAY) goto LBL_ERR;
}
/* if not zero goto step 4 */
if (!mp_iszero(&u)) {
goto top;
}
/* if not zero goto step 4 */
} while (!mp_iszero(&u));
/* now a = C, b = D, gcd == g*v */

86
s_mp_invmod_slow.c
View File

@ -36,60 +36,58 @@ mp_err s_mp_invmod_slow(const mp_int *a, const mp_int *b, mp_int *c)
mp_set(&A, 1uL);
mp_set(&D, 1uL);
top:
/* 4. while u is even do */
while (mp_iseven(&u)) {
/* 4.1 u = u/2 */
if ((err = mp_div_2(&u, &u)) != MP_OKAY) goto LBL_ERR;
do {
/* 4. while u is even do */
while (mp_iseven(&u)) {
/* 4.1 u = u/2 */
if ((err = mp_div_2(&u, &u)) != MP_OKAY) goto LBL_ERR;
/* 4.2 if A or B is odd then */
if (mp_isodd(&A) || mp_isodd(&B)) {
/* A = (A+y)/2, B = (B-x)/2 */
if ((err = mp_add(&A, &y, &A)) != MP_OKAY) goto LBL_ERR;
if ((err = mp_sub(&B, &x, &B)) != MP_OKAY) goto LBL_ERR;
/* 4.2 if A or B is odd then */
if (mp_isodd(&A) || mp_isodd(&B)) {
/* A = (A+y)/2, B = (B-x)/2 */
if ((err = mp_add(&A, &y, &A)) != MP_OKAY) goto LBL_ERR;
if ((err = mp_sub(&B, &x, &B)) != MP_OKAY) goto LBL_ERR;
}
/* A = A/2, B = B/2 */
if ((err = mp_div_2(&A, &A)) != MP_OKAY) goto LBL_ERR;
if ((err = mp_div_2(&B, &B)) != MP_OKAY) goto LBL_ERR;
}
/* A = A/2, B = B/2 */
if ((err = mp_div_2(&A, &A)) != MP_OKAY) goto LBL_ERR;
if ((err = mp_div_2(&B, &B)) != MP_OKAY) goto LBL_ERR;
}
/* 5. while v is even do */
while (mp_iseven(&v)) {
/* 5.1 v = v/2 */
if ((err = mp_div_2(&v, &v)) != MP_OKAY) goto LBL_ERR;
/* 5. while v is even do */
while (mp_iseven(&v)) {
/* 5.1 v = v/2 */
if ((err = mp_div_2(&v, &v)) != MP_OKAY) goto LBL_ERR;
/* 5.2 if C or D is odd then */
if (mp_isodd(&C) || mp_isodd(&D)) {
/* C = (C+y)/2, D = (D-x)/2 */
if ((err = mp_add(&C, &y, &C)) != MP_OKAY) goto LBL_ERR;
if ((err = mp_sub(&D, &x, &D)) != MP_OKAY) goto LBL_ERR;
/* 5.2 if C or D is odd then */
if (mp_isodd(&C) || mp_isodd(&D)) {
/* C = (C+y)/2, D = (D-x)/2 */
if ((err = mp_add(&C, &y, &C)) != MP_OKAY) goto LBL_ERR;
if ((err = mp_sub(&D, &x, &D)) != MP_OKAY) goto LBL_ERR;
}
/* C = C/2, D = D/2 */
if ((err = mp_div_2(&C, &C)) != MP_OKAY) goto LBL_ERR;
if ((err = mp_div_2(&D, &D)) != MP_OKAY) goto LBL_ERR;
}
/* C = C/2, D = D/2 */
if ((err = mp_div_2(&C, &C)) != MP_OKAY) goto LBL_ERR;
if ((err = 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, A = A - C, B = B - D */
if ((err = mp_sub(&u, &v, &u)) != MP_OKAY) goto LBL_ERR;
/* 6. if u >= v then */
if (mp_cmp(&u, &v) != MP_LT) {
/* u = u - v, A = A - C, B = B - D */
if ((err = mp_sub(&u, &v, &u)) != MP_OKAY) goto LBL_ERR;
if ((err = mp_sub(&A, &C, &A)) != MP_OKAY) goto LBL_ERR;
if ((err = mp_sub(&A, &C, &A)) != MP_OKAY) goto LBL_ERR;
if ((err = mp_sub(&B, &D, &B)) != MP_OKAY) goto LBL_ERR;
} else {
/* v - v - u, C = C - A, D = D - B */
if ((err = mp_sub(&v, &u, &v)) != MP_OKAY) goto LBL_ERR;
if ((err = mp_sub(&B, &D, &B)) != MP_OKAY) goto LBL_ERR;
} else {
/* v - v - u, C = C - A, D = D - B */
if ((err = mp_sub(&v, &u, &v)) != MP_OKAY) goto LBL_ERR;
if ((err = mp_sub(&C, &A, &C)) != MP_OKAY) goto LBL_ERR;
if ((err = mp_sub(&C, &A, &C)) != MP_OKAY) goto LBL_ERR;
if ((err = mp_sub(&D, &B, &D)) != MP_OKAY) goto LBL_ERR;
}
if ((err = mp_sub(&D, &B, &D)) != MP_OKAY) goto LBL_ERR;
}
/* if not zero goto step 4 */
if (!mp_iszero(&u)) {
goto top;
}
/* if not zero goto step 4 */
} while (!mp_iszero(&u));
/* now a = C, b = D, gcd == g*v */
@ -111,7 +109,7 @@ top:
/* C is now the inverse */
mp_exch(&C, c);
err = MP_OKAY;
LBL_ERR:
mp_clear_multi(&x, &y, &u, &v, &A, &B, &C, &D, NULL);
return err;