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tls: shrink sp_256_mont_inv_10

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function                                             old     new   delta
sp_256_ecc_mulmod_10                                1237    1251     +14
p256_mod_2                                            32       -     -32
------------------------------------------------------------------------------
(add/remove: 0/1 grow/shrink: 1/0 up/down: 14/-32)            Total: -18 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2021-04-26 18:05:53 +02:00
parent 6381f3d4f6
commit 93b886f54b
1 changed files with 9 additions and 1 deletions
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10
networking/tls_sp_c32.c
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@ -554,11 +554,18 @@ static void sp_256_mont_sqr_10(sp_digit* r, const sp_digit* a, const sp_digit* m
* r Inverse result.
* a Number to invert.
*/
#if 0
/* Mod-2 for the P256 curve. */
static const uint32_t p256_mod_2[8] = {
0xfffffffd,0xffffffff,0xffffffff,0x00000000,
0x00000000,0x00000000,0x00000001,0xffffffff,
};
//Bit pattern:
//2 2 2 2 2 2 2 1...1
//5 5 4 3 2 1 0 9...0 9...1
//543210987654321098765432109876543210987654321098765432109876543210...09876543210...09876543210
//111111111111111111111111111111110000000000000000000000000000000100...00000111111...11111111101
#endif
static void sp_256_mont_inv_10(sp_digit* r, sp_digit* a)
{
sp_digit t[2*10]; //can be just [10]?
@ -567,7 +574,8 @@ static void sp_256_mont_inv_10(sp_digit* r, sp_digit* a)
memcpy(t, a, sizeof(sp_digit) * 10);
for (i = 254; i >= 0; i--) {
sp_256_mont_sqr_10(t, t, p256_mod, p256_mp_mod);
if (p256_mod_2[i / 32] & ((sp_digit)1 << (i % 32)))
/*if (p256_mod_2[i / 32] & ((sp_digit)1 << (i % 32)))*/
if (i >= 224 || i == 192 || (i <= 95 && i != 1))
sp_256_mont_mul_10(t, t, a, p256_mod, p256_mp_mod);
}
memcpy(r, t, sizeof(sp_digit) * 10);