[Asterisk-Dev] MP3 library vs. endian.h

[Chris Albertson]

There is a more simple and portable way to do this that
works on Solaris/Linux/BSD and I'm sure others.  Most
systems define a set of macros to convert byte order and these
marcos "work" becase they are defined differently in BE and LE
machines.  I write code that works on Solaris/SPARC and
Solaris/i386 all the time and never need to use an #ifdef.

Every use of #if doubles your testing requirements as you
must test all combinitorial permutations (or else defer to
Microsoft's methods: "Why test? They'll buy anything, even if
it's broken."

Basically "hton" will take "whatever" and give you a B.E. result
while "ntoh" takes a BE and converts it to your cuurent byte order.
It's OK to chain these as one will always be defined as null.
With some small effort you can eliminate all #if and if() from
your code and depend on the system dot-h files to be correct.
Again, every "if" you remove halves your testing requirement


Here is a quote from the Solaris 9 man page:  (remember "network
byte order" is B.E. as on a SPARC.)

NAME
     byteorder, htonl,  htons,  ntohl,  ntohs  -  convert  values
     between host and network byte order

SYNOPSIS
     #include <sys/types.h>
     #include <netinet/in.h>
     #include <inttypes.h>

     uint32_t htonl(unint32_t hostlong);

     uint16_t htons(uint16_t hostshort);

     uint32_t ntohl(uint32_t netlong);

     uint16_t ntohs(uint16_t netshort);


DESCRIPTION
     These routines convert 16 and 32 bit quantities between net-
     work  byte  order and host byte order. On some architectures
     these routines are defined as NULL  macros  in  the  include
     file  <netinet/in.h>.  On other architectures, if their host
     byte order is different from network byte order, these  rou-
     tines are functional....




--- Rafal Boni <rafal at pobox.com> wrote:
> [...sent once with the wrong From address; apologies to the moderator
> if
>  they see the other message and are confused...]
> 
> Folks:
> 	The way the MP3 library is built, it always defaults to LE mode;
> 	this is because endian.h defines the LITTLE_ENDIAN macro even on
> 	BE systems (it's not supposed to be used to guess endianness by
> 	itself).
> 
> 	The attached patch gets rid of the hokey machine-detection stuff
> 	that never worked and instead uses BYTE_ORDER (I wanted to use 
> 	__BYTE_ORDER or _BYTE_ORDER, but my Linux and NetBSD boxes could
> 	not agree about which was the right one :-/) to determine if we're
> 	a BE or LE system.
> 
> 	This makes the MP3 codec load on my NetBSD/sparc64 (and I'd guess
> 	all other BE systems as well); I still haven't tested it, though.
> 
> 	I still see SIGFPE's from the ILBC and LPC10 codes, but the issue
> 	there doesn't seem to be as clear-cut.
> 
> --rafal
> 
> Index: codecs/mp3/include/L3.h
> ===================================================================
> RCS file: /usr/cvsroot/asterisk/codecs/mp3/include/L3.h,v
> retrieving revision 1.1.1.1
> diff -u -r1.1.1.1 L3.h
> --- codecs/mp3/include/L3.h	12 Feb 2003 13:59:14 -0000	1.1.1.1
> +++ codecs/mp3/include/L3.h	11 Jun 2003 22:44:18 -0000
> @@ -36,27 +36,10 @@
>  #define GLOBAL_GAIN_SCALE (4*15)
>  /* #define GLOBAL_GAIN_SCALE 0 */
>  
> -
> -#ifdef _M_IX86
> -#define LITTLE_ENDIAN 1
> -#endif
> -
> -#ifdef _M_ALPHA
> -#define LITTLE_ENDIAN 1
> -#endif
> -
> -#ifdef sparc
> -#define LITTLE_ENDIAN 0
> -#endif
> -
> -#ifndef LITTLE_ENDIAN
> -#error Layer III LITTLE_ENDIAN must be defined 0 or 1
> -#endif
> -
>  /*-----------------------------------------------------------*/
>  /*---- huffman lookup tables ---*/
>  /* endian dependent !!! */
> -#if LITTLE_ENDIAN
> +#if BYTE_ORDER == LITTLE_ENDIAN
>  typedef union
>  {
>     int ptr;
> _______________________________________________
> Asterisk-Dev mailing list
> Asterisk-Dev at lists.digium.com
> http://lists.digium.com/mailman/listinfo/asterisk-dev


=====
Chris Albertson
  Home:   310-376-1029  chrisalbertson90278 at yahoo.com
  Cell:   310-990-7550
  Office: 310-336-5189  Christopher.J.Albertson at aero.org
  KG6OMK

__________________________________
Do you Yahoo!?
Yahoo! Calendar - Free online calendar with sync to Outlook(TM).
http://calendar.yahoo.com