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Call mp_kronecker from mp_jacobi to save some bytes while keeping the API

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czurnieden 2018-05-11 00:50:52 +02:00 committed by Steffen Jaeckel
parent 9b448bdc08
commit ba786e6b39
1 changed files with 2 additions and 82 deletions
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84
bn_mp_jacobi.c
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@ -14,16 +14,10 @@
*/
/* computes the jacobi c = (a | n) (or Legendre if n is prime)
* HAC pp. 73 Algorithm 2.149
* HAC is wrong here, as the special case of (0 | 1) is not
* handled correctly.
* Kept for legacy reasons, please use mp_kronecker() instead
*/
int mp_jacobi(const mp_int *a, const mp_int *n, int *c)
{
mp_int a1, p1;
int k, s, r, res;
mp_digit residue;
/* if a < 0 return MP_VAL */
if (mp_isneg(a) == MP_YES) {
return MP_VAL;
@ -34,81 +28,7 @@ int mp_jacobi(const mp_int *a, const mp_int *n, int *c)
return MP_VAL;
}
/* step 1. handle case of a == 0 */
if (mp_iszero(a) == MP_YES) {
/* special case of a == 0 and n == 1 */
if (mp_cmp_d(n, 1uL) == MP_EQ) {
*c = 1;
} else {
*c = 0;
}
return MP_OKAY;
}
/* step 2. if a == 1, return 1 */
if (mp_cmp_d(a, 1uL) == MP_EQ) {
*c = 1;
return MP_OKAY;
}
/* default */
s = 0;
/* step 3. write a = a1 * 2**k */
if ((res = mp_init_copy(&a1, a)) != MP_OKAY) {
return res;
}
if ((res = mp_init(&p1)) != MP_OKAY) {
goto LBL_A1;
}
/* divide out larger power of two */
k = mp_cnt_lsb(&a1);
if ((res = mp_div_2d(&a1, k, &a1, NULL)) != MP_OKAY) {
goto LBL_P1;
}
/* step 4. if e is even set s=1 */
if (((unsigned)k & 1u) == 0u) {
s = 1;
} else {
/* else set s=1 if p = 1/7 (mod 8) or s=-1 if p = 3/5 (mod 8) */
residue = n->dp[0] & 7u;
if ((residue == 1u) || (residue == 7u)) {
s = 1;
} else if ((residue == 3u) || (residue == 5u)) {
s = -1;
}
}
/* step 5. if p == 3 (mod 4) *and* a1 == 3 (mod 4) then s = -s */
if (((n->dp[0] & 3u) == 3u) && ((a1.dp[0] & 3u) == 3u)) {
s = -s;
}
/* if a1 == 1 we're done */
if (mp_cmp_d(&a1, 1uL) == MP_EQ) {
*c = s;
} else {
/* n1 = n mod a1 */
if ((res = mp_mod(n, &a1, &p1)) != MP_OKAY) {
goto LBL_P1;
}
if ((res = mp_jacobi(&p1, &a1, &r)) != MP_OKAY) {
goto LBL_P1;
}
*c = s * r;
}
/* done */
res = MP_OKAY;
LBL_P1:
mp_clear(&p1);
LBL_A1:
mp_clear(&a1);
return res;
return mp_kronecker(a,n,c);
}
#endif