implement is_constant for c11: https://gustedt.wordpress.com/2013/08/22/testing-compile-time-constness-and-null-pointers-with-c11s-_generic/

#ifdef _MSC_VER

#include <stdlib.h>
#define bswap_32(x) _byteswap_ulong(x)
#define bswap_64(x) _byteswap_uint64(x)

#elif defined(__APPLE__)

// Mac OS X / Darwin features
#include <libkern/OSByteOrder.h>
#define bswap_32(x) OSSwapInt32(x)
#define bswap_64(x) OSSwapInt64(x)

#elif defined(__sun) || defined(sun)

#include <sys/byteorder.h>
#define bswap_32(x) BSWAP_32(x)
#define bswap_64(x) BSWAP_64(x)

#elif defined(__FreeBSD__)

#include <sys/endian.h>
#define bswap_32(x) bswap32(x)
#define bswap_64(x) bswap64(x)

#elif defined(__OpenBSD__)

#include <sys/types.h>
#define bswap_32(x) swap32(x)
#define bswap_64(x) swap64(x)

#elif defined(__NetBSD__)

#include <sys/types.h>
#include <machine/bswap.h>
#if defined(__BSWAP_RENAME) && !defined(__bswap_32)
#define bswap_32(x) bswap32(x)
#define bswap_64(x) bswap64(x)
#endif

#else

#include <byteswap.h>

#endif

0x00010001
	- add ecb_is_pot32/64.
        - add intptr_t/uintptr_t.
        - add ECB_PTRSIZE.
        - more macros for C/C++ version checks.
        - support C11 atomics for memory fences.
        - support gcc-4.7 atomics for memory fences.
        - support m68k, m88k and sh (patch by Miod Vallat).
        - add ecb_binary16_to_float.

TODO: ecb_restrict_array etc. http://ue.tst.eu/5093eafd713ec5fda776d8065070aa4c.txt
TODO: ffs/clz
64 bit variants of everything
TODO: examples from X for clz/ctz
TODO: arithmetic right shift
TODO: template/generic functions for x32/x64 and so on
TODO: #define ecb_integer_multiples_of(n,d) ((char (*)[d])(n) - (char (*)[d])0)
TODO: generalised shift
TODO: #define ECB_FAST_UNALIGNED_ACCESS
unsigned long gensh(unsigned long v, int x) {
int a, b;
    a = (v << x) & -(((unsigned int)x) < 32);
    x = -x;
    b = (v >> x) & -(((unsigned int)x) < 32);
    return a|b;
}

TODO: read/write unaligned macros
TODO: htonl and friends
TODO: macro to convetr from unsigned to signed "the natural way"
TODO: ecb_deprecated with message
TODO: ecb_static_assert, with message (just like boost), or somesuch, using array-declaration
TODO: alignof