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tls: P256: do not dumplicate sp_256_sub_8()

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function                                             old     new   delta
sp_256_proj_point_dbl_8                              359     374     +15
sp_256_ecc_mulmod_8                                 1159    1171     +12
sp_256_mont_reduce_8                                 245     250      +5
sp_256_mont_dbl_8                                     26      31      +5
sp_256_sub_8_p256_mod                                 43       -     -43
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(add/remove: 0/1 grow/shrink: 4/0 up/down: 37/-43)             Total: -6 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2021-10-06 14:25:10 +02:00
parent 00f2cceb6a
commit 567eefcaf8
1 changed files with 4 additions and 24 deletions
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28
networking/tls_sp_c32.c
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@ -291,10 +291,10 @@ static int sp_256_sub_8(sp_digit* r, const sp_digit* a, const sp_digit* b)
#endif
}
#if ALLOW_ASM && defined(__GNUC__) && defined(__i386__)
/* Sub p256_mod from a into r. (r = a - p256_mod). */
static void sp_256_sub_8_p256_mod(sp_digit* r, const sp_digit* a)
{
#if ALLOW_ASM && defined(__GNUC__) && defined(__i386__)
sp_digit reg;
//p256_mod[7..0] = ffffffff 00000001 00000000 00000000 00000000 ffffffff ffffffff ffffffff
asm volatile (
@ -334,30 +334,10 @@ static void sp_256_sub_8_p256_mod(sp_digit* r, const sp_digit* a)
: "0" (a), "1" (r)
: "memory"
);
#else
const sp_digit* b = p256_mod;
int i;
sp_digit borrow;
borrow = 0;
for (i = 0; i < 8; i++) {
sp_digit w, v;
w = b[i] + borrow;
v = a[i];
if (w != 0) {
v = a[i] - w;
borrow = (v > a[i]);
/* hope compiler detects above as "carry flag set" */
}
/* else: b + borrow == 0, two cases:
* b:ffffffff, borrow:1
* b:00000000, borrow:0
* in either case, r[i] = a[i] and borrow remains unchanged
*/
r[i] = v;
}
#endif
}
#else
# define sp_256_sub_8_p256_mod(r, a) sp_256_sub_8((r), (a), p256_mod)
#endif
/* Multiply a and b into r. (r = a * b) */
static void sp_256_mul_8(sp_digit* r, const sp_digit* a, const sp_digit* b)