source3/include/byteorder.h

   1 /*
   2    Unix SMB/CIFS implementation.
   3    SMB Byte handling
   4    Copyright (C) Andrew Tridgell 1992-1998
   5
   6    This program is free software; you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 2 of the License, or
   9    (at your option) any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with this program; if not, write to the Free Software
  18    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  19 */
  20
  21 #ifndef _BYTEORDER_H
  22 #define _BYTEORDER_H
  23
  24 /*
  25    This file implements macros for machine independent short and
  26    int manipulation
  27
  28 Here is a description of this file that I emailed to the samba list once:
  29
  30 > I am confused about the way that byteorder.h works in Samba. I have
  31 > looked at it, and I would have thought that you might make a distinction
  32 > between LE and BE machines, but you only seem to distinguish between 386
  33 > and all other architectures.
  34 >
  35 > Can you give me a clue?
  36
  37 sure.
  38
  39 The distinction between 386 and other architectures is only there as
  40 an optimisation. You can take it out completely and it will make no
  41 difference. The routines (macros) in byteorder.h are totally byteorder
  42 independent. The 386 optimsation just takes advantage of the fact that
  43 the x86 processors don't care about alignment, so we don't have to
  44 align ints on int boundaries etc. If there are other processors out
  45 there that aren't alignment sensitive then you could also define
  46 CAREFUL_ALIGNMENT=0 on those processors as well.
  47
  48 Ok, now to the macros themselves. I'll take a simple example, say we
  49 want to extract a 2 byte integer from a SMB packet and put it into a
  50 type called uint16 that is in the local machines byte order, and you
  51 want to do it with only the assumption that uint16 is _at_least_ 16
  52 bits long (this last condition is very important for architectures
  53 that don't have any int types that are 2 bytes long)
  54
  55 You do this:
  56
  57 #define CVAL(buf,pos) (((unsigned char *)(buf))[pos])
  58 #define PVAL(buf,pos) ((unsigned)CVAL(buf,pos))
  59 #define SVAL(buf,pos) (PVAL(buf,pos)|PVAL(buf,(pos)+1)<<8)
  60
  61 then to extract a uint16 value at offset 25 in a buffer you do this:
  62
  63 char *buffer = foo_bar();
  64 uint16 xx = SVAL(buffer,25);
  65
  66 We are using the byteoder independence of the ANSI C bitshifts to do
  67 the work. A good optimising compiler should turn this into efficient
  68 code, especially if it happens to have the right byteorder :-)
  69
  70 I know these macros can be made a bit tidier by removing some of the
  71 casts, but you need to look at byteorder.h as a whole to see the
  72 reasoning behind them. byteorder.h defines the following macros:
  73
  74 SVAL(buf,pos) - extract a 2 byte SMB value
  75 IVAL(buf,pos) - extract a 4 byte SMB value
  76 SVALS(buf,pos) signed version of SVAL()
  77 IVALS(buf,pos) signed version of IVAL()
  78
  79 SSVAL(buf,pos,val) - put a 2 byte SMB value into a buffer
  80 SIVAL(buf,pos,val) - put a 4 byte SMB value into a buffer
  81 SSVALS(buf,pos,val) - signed version of SSVAL()
  82 SIVALS(buf,pos,val) - signed version of SIVAL()
  83
  84 RSVAL(buf,pos) - like SVAL() but for NMB byte ordering
  85 RSVALS(buf,pos) - like SVALS() but for NMB byte ordering
  86 RIVAL(buf,pos) - like IVAL() but for NMB byte ordering
  87 RIVALS(buf,pos) - like IVALS() but for NMB byte ordering
  88 RSSVAL(buf,pos,val) - like SSVAL() but for NMB ordering
  89 RSIVAL(buf,pos,val) - like SIVAL() but for NMB ordering
  90 RSIVALS(buf,pos,val) - like SIVALS() but for NMB ordering
  91
  92 it also defines lots of intermediate macros, just ignore those :-)
  93
  94 */
  95
  96 #undef CAREFUL_ALIGNMENT
  97
  98 /* we know that the 386 can handle misalignment and has the "right"
  99    byteorder */
 100 #ifdef __i386__
 101 #define CAREFUL_ALIGNMENT 0
 102 #endif
 103
 104 #ifndef CAREFUL_ALIGNMENT
 105 #define CAREFUL_ALIGNMENT 1
 106 #endif
 107
 108 #define CVAL(buf,pos) ((unsigned)(((const unsigned char *)(buf))[pos]))
 109 #define CVAL_NC(buf,pos) (((unsigned char *)(buf))[pos]) /* Non-const version of CVAL */
 110 #define PVAL(buf,pos) (CVAL(buf,pos))
 111 #define SCVAL(buf,pos,val) (CVAL_NC(buf,pos) = (val))
 112
 113
 114 #if CAREFUL_ALIGNMENT
 115
 116 #define SVAL(buf,pos) (PVAL(buf,pos)|PVAL(buf,(pos)+1)<<8)
 117 #define IVAL(buf,pos) (SVAL(buf,pos)|SVAL(buf,(pos)+2)<<16)
 118 #define SSVALX(buf,pos,val) (CVAL_NC(buf,pos)=(unsigned char)((val)&0xFF),CVAL_NC(buf,pos+1)=(unsigned char)((val)>>8))
 119 #define SIVALX(buf,pos,val) (SSVALX(buf,pos,val&0xFFFF),SSVALX(buf,pos+2,val>>16))
 120 #define SVALS(buf,pos) ((int16)SVAL(buf,pos))
 121 #define IVALS(buf,pos) ((int32)IVAL(buf,pos))
 122 #define SSVAL(buf,pos,val) SSVALX((buf),(pos),((uint16)(val)))
 123 #define SIVAL(buf,pos,val) SIVALX((buf),(pos),((uint32)(val)))
 124 #define SSVALS(buf,pos,val) SSVALX((buf),(pos),((int16)(val)))
 125 #define SIVALS(buf,pos,val) SIVALX((buf),(pos),((int32)(val)))
 126
 127 #else /* CAREFUL_ALIGNMENT */
 128
 129 /* this handles things for architectures like the 386 that can handle
 130    alignment errors */
 131 /*
 132    WARNING: This section is dependent on the length of int16 and int32
 133    being correct
 134 */
 135
 136 /* get single value from an SMB buffer */
 137 #define SVAL(buf,pos) (*(const uint16 *)((const char *)(buf) + (pos)))
 138 #define SVAL_NC(buf,pos) (*(uint16 *)((char *)(buf) + (pos))) /* Non const version of above. */
 139 #define IVAL(buf,pos) (*(const uint32 *)((const char *)(buf) + (pos)))
 140 #define IVAL_NC(buf,pos) (*(uint32 *)((char *)(buf) + (pos))) /* Non const version of above. */
 141 #define SVALS(buf,pos) (*(const int16 *)((const char *)(buf) + (pos)))
 142 #define SVALS_NC(buf,pos) (*(int16 *)((char *)(buf) + (pos))) /* Non const version of above. */
 143 #define IVALS(buf,pos) (*(const int32 *)((const char *)(buf) + (pos)))
 144 #define IVALS_NC(buf,pos) (*(int32 *)((char *)(buf) + (pos))) /* Non const version of above. */
 145
 146 /* store single value in an SMB buffer */
 147 #define SSVAL(buf,pos,val) SVAL_NC(buf,pos)=((uint16)(val))
 148 #define SIVAL(buf,pos,val) IVAL_NC(buf,pos)=((uint32)(val))
 149 #define SSVALS(buf,pos,val) SVALS_NC(buf,pos)=((int16)(val))
 150 #define SIVALS(buf,pos,val) IVALS_NC(buf,pos)=((int32)(val))
 151
 152 #endif /* CAREFUL_ALIGNMENT */
 153
 154 /* now the reverse routines - these are used in nmb packets (mostly) */
 155 #define SREV(x) ((((x)&0xFF)<<8) | (((x)>>8)&0xFF))
 156 #define IREV(x) ((SREV(x)<<16) | (SREV((x)>>16)))
 157
 158 #define RSVAL(buf,pos) SREV(SVAL(buf,pos))
 159 #define RSVALS(buf,pos) SREV(SVALS(buf,pos))
 160 #define RIVAL(buf,pos) IREV(IVAL(buf,pos))
 161 #define RIVALS(buf,pos) IREV(IVALS(buf,pos))
 162 #define RSSVAL(buf,pos,val) SSVAL(buf,pos,SREV(val))
 163 #define RSSVALS(buf,pos,val) SSVALS(buf,pos,SREV(val))
 164 #define RSIVAL(buf,pos,val) SIVAL(buf,pos,IREV(val))
 165 #define RSIVALS(buf,pos,val) SIVALS(buf,pos,IREV(val))
 166
 167 /* Alignment macros. */
 168 #define ALIGN4(p,base) ((p) + ((4 - (PTR_DIFF((p), (base)) & 3)) & 3))
 169 #define ALIGN2(p,base) ((p) + ((2 - (PTR_DIFF((p), (base)) & 1)) & 1))
 170
 171 #endif /* _BYTEORDER_H */