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tls: P256: factor out "multiply then reduce" operation

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function                                             old     new   delta
sp_256_mont_mul_and_reduce_8                           -      44     +44
sp_256_ecc_mulmod_8                                  517     442     -75
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 0/1 up/down: 44/-75)            Total: -31 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2021-12-11 23:27:40 +01:00
parent b240733ae7
commit 27df6aeef2
1 changed files with 13 additions and 7 deletions
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20
networking/tls_sp_c32.c
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@ -1091,6 +1091,17 @@ static void sp_256_mont_sqr_8(sp_digit* r, const sp_digit* a
sp_256_mont_mul_8(r, a, a /*, m, mp*/);
}
static NOINLINE void sp_256_mont_mul_and_reduce_8(sp_digit* r,
const sp_digit* a, const sp_digit* b
/*, const sp_digit* m, sp_digit mp*/)
{
sp_digit rr[2 * 8];
sp_256_mont_mul_8(rr, a, b /*, p256_mod, p256_mp_mod*/);
memset(rr + 8, 0, sizeof(rr) / 2);
sp_512to256_mont_reduce_8(r, rr /*, p256_mod, p256_mp_mod*/);
}
/* Invert the number, in Montgomery form, modulo the modulus (prime) of the
* P256 curve. (r = 1 / a mod m)
*
@ -1186,7 +1197,6 @@ static void sp_256_map_8(sp_point* r, sp_point* p)
{
sp_digit t1[8];
sp_digit t2[8];
sp_digit rr[2 * 8];
sp_256_mont_inv_8(t1, p->z);
@ -1194,18 +1204,14 @@ static void sp_256_map_8(sp_point* r, sp_point* p)
sp_256_mont_mul_8(t1, t2, t1 /*, p256_mod, p256_mp_mod*/);
/* x /= z^2 */
sp_256_mont_mul_8(rr, p->x, t2 /*, p256_mod, p256_mp_mod*/);
memset(rr + 8, 0, sizeof(rr) / 2);
sp_512to256_mont_reduce_8(r->x, rr /*, p256_mod, p256_mp_mod*/);
sp_256_mont_mul_and_reduce_8(r->x, p->x, t2 /*, p256_mod, p256_mp_mod*/);
/* Reduce x to less than modulus */
if (sp_256_cmp_8(r->x, p256_mod) >= 0)
sp_256_sub_8_p256_mod(r->x);
sp_256_norm_8(r->x);
/* y /= z^3 */
sp_256_mont_mul_8(rr, p->y, t1 /*, p256_mod, p256_mp_mod*/);
memset(rr + 8, 0, sizeof(rr) / 2);
sp_512to256_mont_reduce_8(r->y, rr /*, p256_mod, p256_mp_mod*/);
sp_256_mont_mul_and_reduce_8(r->y, p->y, t1 /*, p256_mod, p256_mp_mod*/);
/* Reduce y to less than modulus */
if (sp_256_cmp_8(r->y, p256_mod) >= 0)
sp_256_sub_8_p256_mod(r->y);