extract.h

/*
 * Copyright (c) 1992, 1993, 1994, 1995, 1996
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that: (1) source code distributions
 * retain the above copyright notice and this paragraph in its entirety, (2)
 * distributions including binary code include the above copyright notice and
 * this paragraph in its entirety in the documentation or other materials
 * provided with the distribution, and (3) all advertising materials mentioning
 * features or use of this software display the following acknowledgement:
 * ``This product includes software developed by the University of California,
 * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
 * the University nor the names of its contributors may be used to endorse
 * or promote products derived from this software without specific prior
 * written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 * @(#) $Header: /tcpdump/master/tcpdump/extract.h,v 1.25 2006-01-30 16:20:07 hannes Exp $ (LBL)
 */

/*
 * Macros to extract possibly-unaligned big-endian integral values.
 */
#ifdef LBL_ALIGN
/*
 * The processor doesn't natively handle unaligned loads.
 */
#if defined(__GNUC__) && defined(HAVE___ATTRIBUTE__) && \
    (defined(__alpha) || defined(__alpha__) || \
     defined(__mips) || defined(__mips__))

/*
 * This is a GCC-compatible compiler and we have __attribute__, which
 * we assume that mean we have __attribute__((packed)), and this is
 * MIPS or Alpha, which has instructions that can help when doing
 * unaligned loads.
 *
 * Declare packed structures containing a u_int16_t and a u_int32_t,
 * cast the pointer to point to one of those, and fetch through it;
 * the GCC manual doesn't appear to explicitly say that
 * __attribute__((packed)) causes the compiler to generate unaligned-safe
 * code, but it apppears to do so.
 *
 * We do this in case the compiler can generate code using those
 * instructions to do an unaligned load and pass stuff to "ntohs()" or
 * "ntohl()", which might be better than than the code to fetch the
 * bytes one at a time and assemble them.  (That might not be the
 * case on a little-endian platform, such as DEC's MIPS machines and
 * Alpha machines, where "ntohs()" and "ntohl()" might not be done
 * inline.)
 *
 * We do this only for specific architectures because, for example,
 * at least some versions of GCC, when compiling for 64-bit SPARC,
 * generate code that assumes alignment if we do this.
 *
 * XXX - add other architectures and compilers as possible and
 * appropriate.
 *
 * HP's C compiler, indicated by __HP_cc being defined, supports
 * "#pragma unaligned N" in version A.05.50 and later, where "N"
 * specifies a number of bytes at which the typedef on the next
 * line is aligned, e.g.
 *
 *	#pragma unalign 1
 *	typedef u_int16_t unaligned_u_int16_t;
 *
 * to define unaligned_u_int16_t as a 16-bit unaligned data type.
 * This could be presumably used, in sufficiently recent versions of
 * the compiler, with macros similar to those below.  This would be
 * useful only if that compiler could generate better code for PA-RISC
 * or Itanium than would be generated by a bunch of shifts-and-ORs.
 *
 * DEC C, indicated by __DECC being defined, has, at least on Alpha,
 * an __unaligned qualifier that can be applied to pointers to get the
 * compiler to generate code that does unaligned loads and stores when
 * dereferencing the pointer in question.
 *
 * XXX - what if the native C compiler doesn't support
 * __attribute__((packed))?  How can we get it to generate unaligned
 * accesses for *specific* items?
 */
typedef struct {
	u_int16_t	val;
} __attribute__((packed)) unaligned_u_int16_t;

typedef struct {
	u_int32_t	val;
} __attribute__((packed)) unaligned_u_int32_t;

static inline u_int16_t
EXTRACT_16BITS(const void *p)
{
	return ((u_int16_t)ntohs(((const unaligned_u_int16_t *)(p))->val));
}

static inline u_int32_t
EXTRACT_32BITS(const void *p)
{
	return ((u_int32_t)ntohl(((const unaligned_u_int32_t *)(p))->val));
}

static inline u_int64_t
EXTRACT_64BITS(const void *p)
{
	return ((u_int64_t)(((u_int64_t)ntohl(((const unaligned_u_int32_t *)(p) + 0)->val)) << 32 | \
		((u_int64_t)ntohl(((const unaligned_u_int32_t *)(p) + 1)->val)) << 0));
}

#else /* have to do it a byte at a time */
/*
 * This isn't a GCC-compatible compiler, we don't have __attribute__,
 * or we do but we don't know of any better way with this instruction
 * set to do unaligned loads, so do unaligned loads of big-endian
 * quantities the hard way - fetch the bytes one at a time and
 * assemble them.
 */
#define EXTRACT_16BITS(p) \
	((u_int16_t)((u_int16_t)*((const u_int8_t *)(p) + 0) << 8 | \
		     (u_int16_t)*((const u_int8_t *)(p) + 1)))
#define EXTRACT_32BITS(p) \
	((u_int32_t)((u_int32_t)*((const u_int8_t *)(p) + 0) << 24 | \
		     (u_int32_t)*((const u_int8_t *)(p) + 1) << 16 | \
		     (u_int32_t)*((const u_int8_t *)(p) + 2) << 8 | \
		     (u_int32_t)*((const u_int8_t *)(p) + 3)))
#define EXTRACT_64BITS(p) \
	((u_int64_t)((u_int64_t)*((const u_int8_t *)(p) + 0) << 56 | \
		     (u_int64_t)*((const u_int8_t *)(p) + 1) << 48 | \
		     (u_int64_t)*((const u_int8_t *)(p) + 2) << 40 | \
		     (u_int64_t)*((const u_int8_t *)(p) + 3) << 32 | \
	             (u_int64_t)*((const u_int8_t *)(p) + 4) << 24 | \
		     (u_int64_t)*((const u_int8_t *)(p) + 5) << 16 | \
		     (u_int64_t)*((const u_int8_t *)(p) + 6) << 8 | \
		     (u_int64_t)*((const u_int8_t *)(p) + 7)))
#endif /* must special-case unaligned accesses */
#else /* LBL_ALIGN */
/*
 * The processor natively handles unaligned loads, so we can just
 * cast the pointer and fetch through it.
 */
static inline u_int16_t
EXTRACT_16BITS(const void *p)
{
	return ((u_int16_t)ntohs(*(const u_int16_t *)(p)));
}

static inline u_int32_t
EXTRACT_32BITS(const void *p)
{
	return ((u_int32_t)ntohl(*(const u_int32_t *)(p)));
}

static inline u_int64_t
EXTRACT_64BITS(const void *p)
{
	return ((u_int64_t)(((u_int64_t)ntohl(*((const u_int32_t *)(p) + 0))) << 32 | \
		((u_int64_t)ntohl(*((const u_int32_t *)(p) + 1))) << 0));

}

#endif /* LBL_ALIGN */

#define EXTRACT_24BITS(p) \
	((u_int32_t)((u_int32_t)*((const u_int8_t *)(p) + 0) << 16 | \
		     (u_int32_t)*((const u_int8_t *)(p) + 1) << 8 | \
		     (u_int32_t)*((const u_int8_t *)(p) + 2)))

/*
 * Macros to extract possibly-unaligned little-endian integral values.
 * XXX - do loads on little-endian machines that support unaligned loads?
 */
#define EXTRACT_LE_8BITS(p) (*(p))
#define EXTRACT_LE_16BITS(p) \
	((u_int16_t)((u_int16_t)*((const u_int8_t *)(p) + 1) << 8 | \
		     (u_int16_t)*((const u_int8_t *)(p) + 0)))
#define EXTRACT_LE_32BITS(p) \
	((u_int32_t)((u_int32_t)*((const u_int8_t *)(p) + 3) << 24 | \
		     (u_int32_t)*((const u_int8_t *)(p) + 2) << 16 | \
		     (u_int32_t)*((const u_int8_t *)(p) + 1) << 8 | \
		     (u_int32_t)*((const u_int8_t *)(p) + 0)))
#define EXTRACT_LE_24BITS(p) \
	((u_int32_t)((u_int32_t)*((const u_int8_t *)(p) + 2) << 16 | \
		     (u_int32_t)*((const u_int8_t *)(p) + 1) << 8 | \
		     (u_int32_t)*((const u_int8_t *)(p) + 0)))
#define EXTRACT_LE_64BITS(p) \
	((u_int64_t)((u_int64_t)*((const u_int8_t *)(p) + 7) << 56 | \
		     (u_int64_t)*((const u_int8_t *)(p) + 6) << 48 | \
		     (u_int64_t)*((const u_int8_t *)(p) + 5) << 40 | \
		     (u_int64_t)*((const u_int8_t *)(p) + 4) << 32 | \
	             (u_int64_t)*((const u_int8_t *)(p) + 3) << 24 | \
		     (u_int64_t)*((const u_int8_t *)(p) + 2) << 16 | \
		     (u_int64_t)*((const u_int8_t *)(p) + 1) << 8 | \
		     (u_int64_t)*((const u_int8_t *)(p) + 0)))