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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 1.24 2005/01/15 02:06:50 guy Exp $ (LBL)
22  */
23 
24 /*
25  * Macros to extract possibly-unaligned big-endian integral values.
26  */
27 #ifdef LBL_ALIGN
28 /*
29  * The processor doesn't natively handle unaligned loads.
30  */
31 #ifdef HAVE___ATTRIBUTE__
32 /*
33  * We have __attribute__; we assume that means we have __attribute__((packed)).
34  * Declare packed structures containing a u_int16_t and a u_int32_t,
35  * cast the pointer to point to one of those, and fetch through it;
36  * the GCC manual doesn't appear to explicitly say that
37  * __attribute__((packed)) causes the compiler to generate unaligned-safe
38  * code, but it apppears to do so.
39  *
40  * We do this in case the compiler can generate, for this instruction set,
41  * better code to do an unaligned load and pass stuff to "ntohs()" or
42  * "ntohl()" than the code to fetch the bytes one at a time and
43  * assemble them.  (That might not be the case on a little-endian platform,
44  * where "ntohs()" and "ntohl()" might not be done inline.)
45  */
46 typedef struct {
47 	u_int16_t	val;
48 } __attribute__((packed)) unaligned_u_int16_t;
49 
50 typedef struct {
51 	u_int32_t	val;
52 } __attribute__((packed)) unaligned_u_int32_t;
53 
54 #define EXTRACT_16BITS(p) \
55 	((u_int16_t)ntohs(((const unaligned_u_int16_t *)(p))->val))
56 #define EXTRACT_32BITS(p) \
57 	((u_int32_t)ntohl(((const unaligned_u_int32_t *)(p))->val))
58 #define EXTRACT_64BITS(p) \
59 	((u_int64_t)(((u_int64_t)ntohl(((const unaligned_u_int32_t *)(p) + 0)->val)) << 32 | \
60 		     ((u_int64_t)ntohl(((const unaligned_u_int32_t *)(p) + 1)->val)) << 0))
61 
62 #else /* HAVE___ATTRIBUTE__ */
63 /*
64  * We don't have __attribute__, so do unaligned loads of big-endian
65  * quantities the hard way - fetch the bytes one at a time and
66  * assemble them.
67  */
68 #define EXTRACT_16BITS(p) \
69 	((u_int16_t)((u_int16_t)*((const u_int8_t *)(p) + 0) << 8 | \
70 		     (u_int16_t)*((const u_int8_t *)(p) + 1)))
71 #define EXTRACT_32BITS(p) \
72 	((u_int32_t)((u_int32_t)*((const u_int8_t *)(p) + 0) << 24 | \
73 		     (u_int32_t)*((const u_int8_t *)(p) + 1) << 16 | \
74 		     (u_int32_t)*((const u_int8_t *)(p) + 2) << 8 | \
75 		     (u_int32_t)*((const u_int8_t *)(p) + 3)))
76 #define EXTRACT_64BITS(p) \
77 	((u_int64_t)((u_int64_t)*((const u_int8_t *)(p) + 0) << 56 | \
78 		     (u_int64_t)*((const u_int8_t *)(p) + 1) << 48 | \
79 		     (u_int64_t)*((const u_int8_t *)(p) + 2) << 40 | \
80 		     (u_int64_t)*((const u_int8_t *)(p) + 3) << 32 | \
81 	             (u_int64_t)*((const u_int8_t *)(p) + 4) << 24 | \
82 		     (u_int64_t)*((const u_int8_t *)(p) + 5) << 16 | \
83 		     (u_int64_t)*((const u_int8_t *)(p) + 6) << 8 | \
84 		     (u_int64_t)*((const u_int8_t *)(p) + 7)))
85 #endif /* HAVE___ATTRIBUTE__ */
86 #else /* LBL_ALIGN */
87 /*
88  * The processor natively handles unaligned loads, so we can just
89  * cast the pointer and fetch through it.
90  */
91 #define EXTRACT_16BITS(p) \
92 	((u_int16_t)ntohs(*(const u_int16_t *)(p)))
93 #define EXTRACT_32BITS(p) \
94 	((u_int32_t)ntohl(*(const u_int32_t *)(p)))
95 #define EXTRACT_64BITS(p) \
96 	((u_int64_t)(((u_int64_t)ntohl(*((const u_int32_t *)(p) + 0))) << 32 | \
97 		     ((u_int64_t)ntohl(*((const u_int32_t *)(p) + 1))) << 0))
98 #endif /* LBL_ALIGN */
99 
100 #define EXTRACT_24BITS(p) \
101 	((u_int32_t)((u_int32_t)*((const u_int8_t *)(p) + 0) << 16 | \
102 		     (u_int32_t)*((const u_int8_t *)(p) + 1) << 8 | \
103 		     (u_int32_t)*((const u_int8_t *)(p) + 2)))
104 
105 /*
106  * Macros to extract possibly-unaligned little-endian integral values.
107  * XXX - do loads on little-endian machines that support unaligned loads?
108  */
109 #define EXTRACT_LE_8BITS(p) (*(p))
110 #define EXTRACT_LE_16BITS(p) \
111 	((u_int16_t)((u_int16_t)*((const u_int8_t *)(p) + 1) << 8 | \
112 		     (u_int16_t)*((const u_int8_t *)(p) + 0)))
113 #define EXTRACT_LE_32BITS(p) \
114 	((u_int32_t)((u_int32_t)*((const u_int8_t *)(p) + 3) << 24 | \
115 		     (u_int32_t)*((const u_int8_t *)(p) + 2) << 16 | \
116 		     (u_int32_t)*((const u_int8_t *)(p) + 1) << 8 | \
117 		     (u_int32_t)*((const u_int8_t *)(p) + 0)))
118 #define EXTRACT_LE_64BITS(p) \
119 	((u_int64_t)((u_int64_t)*((const u_int8_t *)(p) + 7) << 56 | \
120 		     (u_int64_t)*((const u_int8_t *)(p) + 6) << 48 | \
121 		     (u_int64_t)*((const u_int8_t *)(p) + 5) << 40 | \
122 		     (u_int64_t)*((const u_int8_t *)(p) + 4) << 32 | \
123 	             (u_int64_t)*((const u_int8_t *)(p) + 3) << 24 | \
124 		     (u_int64_t)*((const u_int8_t *)(p) + 2) << 16 | \
125 		     (u_int64_t)*((const u_int8_t *)(p) + 1) << 8 | \
126 		     (u_int64_t)*((const u_int8_t *)(p) + 0)))
127