[git commit] tls: P256: simplify sp_256_mont_inv_8 (no need for a temporary)

[Denys Vlasenko]

commit: https://git.busybox.net/busybox/commit/?id=cfb615781df5c7439fe0060a85e6b6a56d10dc7f
branch: https://git.busybox.net/busybox/commit/?id=refs/heads/master

function                                             old     new   delta
sp_256_ecc_mulmod_8                                  543     517     -26

Signed-off-by: Denys Vlasenko <vda.linux at googlemail.com>
---
 networking/tls_sp_c32.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/networking/tls_sp_c32.c b/networking/tls_sp_c32.c
index 37e1cfa1c..9bd5c6832 100644
--- a/networking/tls_sp_c32.c
+++ b/networking/tls_sp_c32.c
@@ -938,7 +938,7 @@ static void sp_256_mont_sqr_8(sp_digit* r, const sp_digit* a
 /* Invert the number, in Montgomery form, modulo the modulus (prime) of the
  * P256 curve. (r = 1 / a mod m)
  *
- * r   Inverse result.
+ * r   Inverse result. Must not coincide with a.
  * a   Number to invert.
  */
 #if 0
@@ -952,17 +952,15 @@ static void sp_256_mont_sqr_8(sp_digit* r, const sp_digit* a
 #endif
 static void sp_256_mont_inv_8(sp_digit* r, sp_digit* a)
 {
-	sp_digit t[8];
 	int i;
 
-	memcpy(t, a, sizeof(sp_digit) * 8);
+	memcpy(r, a, sizeof(sp_digit) * 8);
 	for (i = 254; i >= 0; i--) {
-		sp_256_mont_sqr_8(t, t /*, p256_mod, p256_mp_mod*/);
+		sp_256_mont_sqr_8(r, r /*, p256_mod, p256_mp_mod*/);
 		/*if (p256_mod_2[i / 32] & ((sp_digit)1 << (i % 32)))*/
 		if (i >= 224 || i == 192 || (i <= 95 && i != 1))
-			sp_256_mont_mul_8(t, t, a /*, p256_mod, p256_mp_mod*/);
+			sp_256_mont_mul_8(r, r, a /*, p256_mod, p256_mp_mod*/);
 	}
-	memcpy(r, t, sizeof(sp_digit) * 8);
 }
 
 /* Multiply a number by Montogmery normalizer mod modulus (prime).