Merge dashpay#787: Use preprocessor macros instead of autoconf to det…

…ect endianness

0dccf98 Use preprocessor macros instead of autoconf to detect endianness (Tim Ruffing)

Pull request description:

  This does not fix any particular issue but it's preferable to not
  rely on autoconf. This avoids endianness mess for users on BE hosts
  if they use their build without autoconf.

  The macros are carefully written to err on the side of the caution,
  e.g., we #error if the user manually configures a different endianness
  than what we detect.

  Supersedes dashpay#770 .

ACKs for top commit:
  sipa:
    ACK 0dccf98
  gmaxwell:
    ACK 0dccf98

Tree-SHA512: 6779458de5cb6eaef2ac37f9d4b8fa6c9b299f58f6e5b72f2b0d7e36c12ea06074e483acfb85085a147e0f4b51cd67d897f61a67250ec1cea284a0f7680eb2e8

configure.ac

@@ -421,8 +421,6 @@ if test x"$enable_module_recovery" = x"yes"; then
   AC_DEFINE(ENABLE_MODULE_RECOVERY, 1, [Define this symbol to enable the ECDSA pubkey recovery module])
 fi
 
-AC_C_BIGENDIAN()
-
 if test x"$use_external_asm" = x"yes"; then
   AC_DEFINE(USE_EXTERNAL_ASM, 1, [Define this symbol if an external (non-inline) assembly implementation is used])
 fi

src/hash_impl.h

@@ -8,6 +8,7 @@
 #define SECP256K1_HASH_IMPL_H
 
 #include "hash.h"
+#include "util.h"
 
 #include <stdlib.h>
 #include <stdint.h>
@@ -27,9 +28,9 @@
     (h) = t1 + t2; \
 } while(0)
 
-#ifdef WORDS_BIGENDIAN
+#if defined(SECP256K1_BIG_ENDIAN)
 #define BE32(x) (x)
-#else
+#elif defined(SECP256K1_LITTLE_ENDIAN)
 #define BE32(p) ((((p) & 0xFF) << 24) | (((p) & 0xFF00) << 8) | (((p) & 0xFF0000) >> 8) | (((p) & 0xFF000000) >> 24))
 #endif
 

src/util.h

@@ -176,6 +176,20 @@ static SECP256K1_INLINE void *manual_alloc(void** prealloc_ptr, size_t alloc_siz
 # define SECP256K1_GNUC_EXT
 #endif
 
+#if defined(__BYTE_ORDER__)
+# if defined(__ORDER_LITTLE_ENDIAN__) && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ && !defined(SECP256K1_LITTLE_ENDIAN)
+#  define SECP256K1_LITTLE_ENDIAN
+# elif defined(__ORDER_BIG_ENDIAN__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__ && !defined(SECP256K1_BIG_ENDIAN)
+#  define SECP256K1_BIG_ENDIAN
+# endif
+#endif
+#if defined(_MSC_VER) && defined(_WIN32) && !defined(SECP256K1_LITTLE_ENDIAN)
+# define SECP256K1_LITTLE_ENDIAN
+#endif
+#if defined(SECP256K1_LITTLE_ENDIAN) == defined(SECP256K1_BIG_ENDIAN)
+# error Please make sure that either SECP256K1_LITTLE_ENDIAN or SECP256K1_BIG_ENDIAN is set, see src/util.h.
+#endif
+
 /* Zero memory if flag == 1. Flag must be 0 or 1. Constant time. */
 static SECP256K1_INLINE void memczero(void *s, size_t len, int flag) {
     unsigned char *p = (unsigned char *)s;