void memmove_wrap(char *dst, const char *src, size_t n, const char *start, const char *end)
{
	char *srcend = src+n;
	if (srcend >= end) srcend -= end-start;

	if ((dst < src && (src < srcend || srcend <= dst)) ||
		(src+n <= dst))
	{
		/* dst isn't in [src; src+n[
		 *       src     srcend
		 *  start|       |  end
		 *  v    v       v  v
		 * |-----ssssssss---|
		 * |---dddddddd-----|
		 *     ^
		 *     dst
		 * or
		 * |ss-----sssssssss|
		 * |d-----dddddddddd|
		 * or
		 * |--ssssssssss----|
		 * |ddddddd------ddd| */

#if 0   /* slow */
		while (n--)
		{
			*dst++ = *src++;
			if (dst == end)
				dst = start;
			if (src == end)
				src = start;
		}
#else
        char *dstend = dst+n;
        if (dstend >= end) dstend -= end-start;

        bool src_wraps = src > srcend;
        bool dst_wraps = dst > dstend;

        if (dst < src)
        {
            if (!src_wraps)
            {
                /* src doesn't wrap, dst < src so dst doesn't wrap */
                memmove(dst, src, n);
            }
            else /* srcend <= dst */
            {
                /* src does wrap */

                size_t first_move = end - src;
                memmove(dst, src, first_move);

                if (!dst_wraps)
                {
                    /* dst doesn't wrap */
                    memmove(dst + first_move, start, n - first_move);
                }
                else
                {
                    /* dst does wrap */
                    size_t second_move = end - dst + first_move;
                    memmove(dst + first_move, start, second_move);
                    size_t third_move = n - second_move - first_move;
                    memmove(start, start + second_move, third_move);
                }
            }
        }
        else /* src+n <= dst */
        {
            /* TODO */
        }
#endif
	}
	else if (src != dst)
	{
		/* dst is in [src; src+n[
		 * |-----ssssssss---|
		 * |------dddddddd--|
		 * or
		 * |ss-----sssssssss|
		 * |-ddddddddddd----|
		 * or
		 * |ss-----sssssssss|
		 * |dddd-----ddddddd| */
		/* copy non overlapping data first */
		size_t offset = srcend-dst;
		if (offset < 0) offset += end-start;
		char *dstoffset = dst+offset;
		if (dstoffset >= end) dstoffset -= end-start;
		const char *srcoffset = src+offset;
		if (srcoffset >= end) srcoffset -= end-start;
		memmove_wrap(dstoffset, srcoffset, n-offset, start, end);
		memmove_wrap(dst, src, offset, start, end);
	}
}