+#define __constant_swap16(x) ((uint16_t)( \
+ (((uint16_t)(x) & (uint16_t)0x00ffU) << 8) | \
+ (((uint16_t)(x) & (uint16_t)0xff00U) >> 8)))
+
+#define __constant_swap32(x) ((uint32_t)( \
+ (((uint32_t)(x) & (uint32_t)0x000000ffUL) << 24) | \
+ (((uint32_t)(x) & (uint32_t)0x0000ff00UL) << 8) | \
+ (((uint32_t)(x) & (uint32_t)0x00ff0000UL) >> 8) | \
+ (((uint32_t)(x) & (uint32_t)0xff000000UL) >> 24)))
+
+#define __constant_swap64(x) ((uint64_t)( \
+ (((uint64_t)(x) & (uint64_t)0x00000000000000ffULL) << 56) | \
+ (((uint64_t)(x) & (uint64_t)0x000000000000ff00ULL) << 40) | \
+ (((uint64_t)(x) & (uint64_t)0x0000000000ff0000ULL) << 24) | \
+ (((uint64_t)(x) & (uint64_t)0x00000000ff000000ULL) << 8) | \
+ (((uint64_t)(x) & (uint64_t)0x000000ff00000000ULL) >> 8) | \
+ (((uint64_t)(x) & (uint64_t)0x0000ff0000000000ULL) >> 24) | \
+ (((uint64_t)(x) & (uint64_t)0x00ff000000000000ULL) >> 40) | \
+ (((uint64_t)(x) & (uint64_t)0xff00000000000000ULL) >> 56)))
+
+/*
+ * This returns a constant expression while determining if an argument is
+ * a constant expression, most importantly without evaluating the argument.
+ */
+#define __is_constant(x) \
+ (sizeof(int) == sizeof(*(1 ? ((void*)((long)(x) * 0l)) : (int*)1)))
+
+#define __eval_once(func, x) \
+ ({ __typeof__(x) __x = x; func(__x); })