[git commit] tls: P256: do not dumplicate sp_256_sub_8()

[Denys Vlasenko]

commit: https://git.busybox.net/busybox/commit/?id=567eefcaf8712b72c3cd5b45aa013ff1eb45d235
branch: https://git.busybox.net/busybox/commit/?id=refs/heads/master

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
------------------------------------------------------------------------------
(add/remove: 0/1 grow/shrink: 4/0 up/down: 37/-43)             Total: -6 bytes

Signed-off-by: Denys Vlasenko <vda.linux at googlemail.com>
---
 networking/tls_sp_c32.c | 26 +++-----------------------
 1 file changed, 3 insertions(+), 23 deletions(-)

diff --git a/networking/tls_sp_c32.c b/networking/tls_sp_c32.c
index 6fca2aad8..17fc05f63 100644
--- a/networking/tls_sp_c32.c
+++ b/networking/tls_sp_c32.c
@@ -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;
-	}
+# 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)