Curve25519 converted from inline assembly to asm only

Fixed large values (top bit set) in tables to be negative as the type is
signed.
Put C++ protection around function prototypes in fe_operations.h.

src/include.am

@@ -372,6 +372,9 @@ if BUILD_CURVE25519_SMALL
 src_libwolfssl_la_SOURCES += wolfcrypt/src/fe_low_mem.c
 else
 src_libwolfssl_la_SOURCES += wolfcrypt/src/fe_operations.c
+if BUILD_INTELASM
+src_libwolfssl_la_SOURCES += wolfcrypt/src/fe_x25519_asm.S
+endif
 endif
 endif
 
@@ -382,6 +385,9 @@ else
 src_libwolfssl_la_SOURCES += wolfcrypt/src/ge_operations.c
 if !BUILD_FEMATH
 src_libwolfssl_la_SOURCES += wolfcrypt/src/fe_operations.c
+if BUILD_INTELASM
+src_libwolfssl_la_SOURCES += wolfcrypt/src/fe_x25519_asm.S
+endif
 endif
 endif
 endif

wolfcrypt/src/fe_operations.c

@@ -42,7 +42,7 @@
 #endif
 
 #ifdef CURVED25519_X64
-#include "fe_x25519_x64.i"
+/* Assumbly code in fe_x25519_asm.* */
 #elif defined(CURVED25519_128BIT)
 #include "fe_x25519_128.i"
 #else

wolfcrypt/src/include.am

@@ -40,8 +40,7 @@ EXTRA_DIST += \
               wolfcrypt/src/fp_sqr_comba_8.i \
               wolfcrypt/src/fp_sqr_comba_9.i \
               wolfcrypt/src/fp_sqr_comba_small_set.i \
-              wolfcrypt/src/fe_x25519_128.i \
-              wolfcrypt/src/fe_x25519_x64.i
+              wolfcrypt/src/fe_x25519_128.i
 
 EXTRA_DIST += wolfcrypt/src/port/ti/ti-aes.c \
               wolfcrypt/src/port/ti/ti-des3.c \

wolfssl/wolfcrypt/fe_operations.h

@@ -47,6 +47,10 @@ t[0]+2^26 t[1]+2^51 t[2]+2^77 t[3]+2^102 t[4]+...+2^230 t[9].
 Bounds on each t[i] vary depending on context.
 */
 
+#ifdef __cplusplus
+    extern "C" {
+#endif
+
 #if defined(CURVE25519_SMALL) || defined(ED25519_SMALL)
     #define F25519_SIZE 32
 
@@ -181,6 +185,11 @@ WOLFSSL_LOCAL void fprime_mul(byte *r, const byte *a, const byte *b,
 WOLFSSL_LOCAL void fprime_copy(byte *x, const byte *a);
 
 #endif /* CURVE25519_SMALL || ED25519_SMALL */
+
+#ifdef __cplusplus
+    } /* extern "C" */
+#endif
+
 #endif /* HAVE_CURVE25519 || HAVE_ED25519 */
 
 #endif /* WOLF_CRYPT_FE_OPERATIONS_H */