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extract.h
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extract.h
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/*
* 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)))