Endianness, beautifully done

My performance enthusiastic friend wrote an excellent article (with working code) in how to determine the system's endianness and how to do swap bytes.

Out of curiosity, I browsed the Tcl source code to see how Tcl work out the global variable tcl_platform(byteOrder). Below code is extracted from tclBasic.c under the Tcl8.4.x source base. It is done beautifully and it really showed what Beautiful Code is all about.

     .....

     union {
         char c[sizeof(short)];
         short s;
     } order;

     .....

     /*
      * Compute the byte order of this machine.
      */

     order.s = 1;
     Tcl_SetVar2(interp, "tcl_platform", "byteOrder",
             ((order.c[0] == 1) ? "littleEndian" : "bigEndian"),
             TCL_GLOBAL_ONLY);

I extracted part of the code for verification.

#include 
union {
         char c[sizeof(short)];
         short s;
} order;

int main(void)
{
         order.s=1;
         printf("%s\n",order.c[0]==1 ? "littleEndian" : "bigEndian");
         exit(0);
}

On my Intel notebook, it is littleEndian and on the SPARC it is bigEndian. Of course it tallies with the Tcl global variable tcl_platform(byteOrder). In case you a Perl guy, this is how you can do it:

$is_big = unpack("h*", pack("s", 1)) =~ /01/;
$is_little = unpack("h*", pack("s", 1)) =~ /^1/;