extract.h revision 127668 
1/*
2 * Copyright (c) 1992, 1993, 1994, 1995, 1996
3 *	The Regents of the University of California.  All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that: (1) source code distributions
7 * retain the above copyright notice and this paragraph in its entirety, (2)
8 * distributions including binary code include the above copyright notice and
9 * this paragraph in its entirety in the documentation or other materials
10 * provided with the distribution, and (3) all advertising materials mentioning
11 * features or use of this software display the following acknowledgement:
12 * ``This product includes software developed by the University of California,
13 * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
14 * the University nor the names of its contributors may be used to endorse
15 * or promote products derived from this software without specific prior
16 * written permission.
17 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
18 * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
19 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
20 *
21 * @(#) $Header: /tcpdump/master/tcpdump/extract.h,v 1.19 2002/12/11 07:13:51 guy Exp $ (LBL)
22 */
23
24/* Network to host order macros */
25
26#ifdef LBL_ALIGN
27/*
28 * The processor doesn't natively handle unaligned loads.
29 */
30#ifdef HAVE___ATTRIBUTE__
31/*
32 * We have __attribute__; we assume that means we have __attribute__((packed)).
33 * Declare packed structures containing a u_int16_t and a u_int32_t,
34 * cast the pointer to point to one of those, and fetch through it;
35 * the GCC manual doesn't appear to explicitly say that
36 * __attribute__((packed)) causes the compiler to generate unaligned-safe
37 * code, but it apppears to do so.
38 *
39 * We do this in case the compiler can generate, for this instruction set,
40 * better code to do an unaligned load and pass stuff to "ntohs()" or
41 * "ntohl()" than the code to fetch the bytes one at a time and
42 * assemble them.  (That might not be the case on a little-endian platform,
43 * where "ntohs()" and "ntohl()" might not be done inline.)
44 */
45typedef struct {
46	u_int16_t	val;
47} __attribute__((packed)) unaligned_u_int16_t;
48
49typedef struct {
50	u_int32_t	val;
51} __attribute__((packed)) unaligned_u_int32_t;
52
53#define EXTRACT_16BITS(p) \
54	((u_int16_t)ntohs(((const unaligned_u_int16_t *)(p))->val))
55#define EXTRACT_32BITS(p) \
56	((u_int32_t)ntohl(((const unaligned_u_int32_t *)(p))->val))
57#else /* HAVE___ATTRIBUTE__ */
58/*
59 * We don't have __attribute__, so do unaligned loads of big-endian
60 * quantities the hard way - fetch the bytes one at a time and
61 * assemble them.
62 */
63#define EXTRACT_16BITS(p) \
64	((u_int16_t)((u_int16_t)*((const u_int8_t *)(p) + 0) << 8 | \
65		     (u_int16_t)*((const u_int8_t *)(p) + 1)))
66#define EXTRACT_32BITS(p) \
67	((u_int32_t)((u_int32_t)*((const u_int8_t *)(p) + 0) << 24 | \
68		     (u_int32_t)*((const u_int8_t *)(p) + 1) << 16 | \
69		     (u_int32_t)*((const u_int8_t *)(p) + 2) << 8 | \
70		     (u_int32_t)*((const u_int8_t *)(p) + 3)))
71#endif /* HAVE___ATTRIBUTE__ */
72#else /* LBL_ALIGN */
73/*
74 * The processor natively handles unaligned loads, so we can just
75 * cast the pointer and fetch through it.
76 */
77#define EXTRACT_16BITS(p) \
78	((u_int16_t)ntohs(*(const u_int16_t *)(p)))
79#define EXTRACT_32BITS(p) \
80	((u_int32_t)ntohl(*(const u_int32_t *)(p)))
81#endif /* LBL_ALIGN */
82
83#define EXTRACT_24BITS(p) \
84	((u_int32_t)((u_int32_t)*((const u_int8_t *)(p) + 0) << 16 | \
85		     (u_int32_t)*((const u_int8_t *)(p) + 1) << 8 | \
86		     (u_int32_t)*((const u_int8_t *)(p) + 2)))
87
88/* Little endian protocol host order macros */
89
90#define EXTRACT_LE_8BITS(p) (*(p))
91#define EXTRACT_LE_16BITS(p) \
92	((u_int16_t)((u_int16_t)*((const u_int8_t *)(p) + 1) << 8 | \
93		     (u_int16_t)*((const u_int8_t *)(p) + 0)))
94#define EXTRACT_LE_32BITS(p) \
95	((u_int32_t)((u_int32_t)*((const u_int8_t *)(p) + 3) << 24 | \
96		     (u_int32_t)*((const u_int8_t *)(p) + 2) << 16 | \
97		     (u_int32_t)*((const u_int8_t *)(p) + 1) << 8 | \
98		     (u_int32_t)*((const u_int8_t *)(p) + 0)))
99