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GLAST/LAT > DAQ and FSW > FSW > Doxygen Index > LSF / V2-0-6

Constituent: lsfprint     Tag: sun-gcc

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LSF_endianness.h File Reference

Provides definitions of the ENDIANNESS of the target machine. The symbols ENDIANNESS_IS_LITTLE and ENDIANNESS_IS_BIG should be used in preprocessing directives to determine the endianness of the machine, while the symbol ENDIANNESS can be more easily used in 'C' code. More...

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Defines
#define	ENDIANNESS_K_UNKNOWN   0
	Value of ENDIANNESS the endianness of the target is undefined.
#define	ENDIANNESS_K_LITTLE   1
	Value of ENDIANNESS if the target is a little endian machine.
#define	ENDIANNESS_K_BIG   2
	Value of ENDIANNESS if the target is a big endian machine machine.
#define	ENDIANNESS   ENDIANNESS_K_UNKNOWN
	ENDINANESS assumes one of the values,
#define	ENDIANNESS_IS_LITTLE   ENDIANNESS_K_UNKNOWN
	Defined and set to a non-zero value, ENDIANNESS_K_LITTLE, if the target is a little endian machine.
#define	ENDIANNESS_IS_BIG   ENDIANNESS_K_UNKNOWN
	Defined and set to a non-zero value, ENDIANNESS_BIG, if the target is a big endian machine.

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Detailed Description

Provides definitions of the ENDIANNESS of the target machine. The symbols ENDIANNESS_IS_LITTLE and ENDIANNESS_IS_BIG should be used in preprocessing directives to determine the endianness of the machine, while the symbol ENDIANNESS can be more easily used in 'C' code.

Author:

JJRussell - russell@slac.stanford.edu

   CVS $Id: LSF_endianness.h,v 1.4 2006/02/15 21:31:10 russell Exp $

SYNOPSIS

One of two symbols are defined

• ENDIANNESS_IS_LITTLE
• ENDIANNESS_IS_BIG.

As a convenience to the programmer, an overall symbol, ENDIANNESS is also defined. It will take on one of the three values.

• ENDIANNESS_K_UNKNOWN
• ENDIANNESS_K_LITTLE
• ENDIANNESS_K_BIG

USAGE

One should use this as follows

    #if   ENDIANNESS_IS_LITTLE

      / * Do little endian kind of things * /

    #elif ENDIANNESS_IS_BIG

      / * Do big endian kind of things * /

    #else

    #error _FILE_ Endianness not determined in this file

    #endif

It is recommended that both BIG and LITTLE conditions are tested for. This can save one from embarrassing typographical errors. For example, consider the consequences of the following

    #if ENDIANESS_IS_LITTLE

       / * Do little endian kind of things * /

    #else

       / * Do big endian kind of things * /

    #endif

It takes a keen eye to note the misspelling of ENDIANNESS_IS_LITTLE as ENDIANESS_IS_LITTLE. Since there is no such symbol as ENDIANESS_IS_LITTLE, the 'big' endian kind of things will always be done.

It is also recommended that one use #if preprocessor directive over the #ifdef form. Either works with the current implementation, but future implementations reserves the right to support only the # if form.

TARGET PLATFORMS

All FSW supported platforms.

This file has been cloned into this package from EDS (which in turn was cloned from PBI). This is in an attempt to make this package independent of EDS and PBI.

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Define Documentation

#define ENDIANNESS   ENDIANNESS_K_UNKNOWN

ENDINANESS assumes one of the values, ENDIANNESS_K_LITTLE ENDIANNESS_K_BIG ENDIANNESS_K_UNKNOWN. Note: Since DOXYGEN does not have access to the full set of compile time preprocessor symbols, ENDIANNESS will appear to be defined as ENDIANNESS_K_UNKNOWN. Warning: It is not recommended that this symbol be used in preprocessor directives to determine the endianness of the machine. Use ENDIANNESS_IS_LITTLE or ENDIANNESS_IS_BIG. Why? To do this correctly one must use the following long-winded style: if defined (ENDIANNESS) && (ENDIANNESS == ENDIANNESS_K_LITTLE) { . . } elif defined (ENDIANNESS) && (ENDIANNESS == ENDIANNESS_K_BIG) { . . } else { . / * Endianness unknown * / } The check for ENDIANNESS being defined is mandatory for robustness. If the user forgets to include "LSF/Endiannness.h", all the ENDIANNESS symbols are, in fact, undefined. Without the check that ENDIANNESS is defined, the simple check of (ENDIANNESS == ENDIANNESS_K_LITTLE) will always succeed, causing the big endian if clause to always be taken. If the code is developed on a big endian machine, it is only when the code is ported to a little endian machine will the problem show up as malfunctioning code which the poor developer will eventually trace to the ill-constructed endianness determination.

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