tls: P256: do not dumplicate sp_256_sub_8()

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@googlemail.com>

1 files 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)