Re: [PATCH 07/19] compat: add endianness helpers

From: Thomas Rast <tr@thomasrast.ch>
Date: Oct 26, 2013, 07:55 UTC
Message-ID: <87txg4sbyf.fsf@linux-k42r.v.cablecom.net>
In-Reply-To: <20131024180157.GG24180@sigill.intra.peff.net>

Jeff King <peff@peff.net> writes:

> From: Vicent Marti <tanoku@gmail.com>
>
> The POSIX standard doesn't currently define a `nothll`/`htonll`

typo: ntohll

> function pair to perform network-to-host and host-to-network
> swaps of 64-bit data. These 64-bit swaps are necessary for the on-disk
> storage of EWAH bitmaps if they are not in native byte order.

[...]

> +#		include <byteswap.h>

Do we need a hack on top similar to what ntoh_l and hton_l do, for platforms that do not support unaligned access?

---- read-cache.c:1316 ----
#ifndef NEEDS_ALIGNED_ACCESS
#define ntoh_s(var) ntohs(var)
#define ntoh_l(var) ntohl(var)
#else
static inline uint16_t ntoh_s_force_align(void *p)
{
	uint16_t x;
	memcpy(&x, p, sizeof(x));
	return ntohs(x);
}
static inline uint32_t ntoh_l_force_align(void *p)
{
	uint32_t x;
	memcpy(&x, p, sizeof(x));
	return ntohl(x);
}
#define ntoh_s(var) ntoh_s_force_align(&(var))
#define ntoh_l(var) ntoh_l_force_align(&(var))
#endif

-- 
Thomas Rast
tr@thomasrast.ch