W.J. Metzger wrote:
>Here is a small C routine to copy a file swapping the bytes, i.e.,
>changing the endian-ness.
>
The size of the cell within which you reverse the bytes depends on the
I/O list item. If you are reading an 8-byte real, you reverse a block
of 8 bytes. If you are reading a 2-byte integer, only 2 bytes are
reversed. In general a file contains a mixture of different sizes of
data, so a simplistic program like the one below has pretty limited use.
(It is also not very optimal code for most modern processors, but that's
an unrelated issue.)
>
>Some (well at least one, Intel) Fortran compilers have a
>mechanism for changing the endian-ness when reading or writing a file.
>
I'd guess "some" is really "several". This is the right way to do it.
The I/O operation knows, on an item by item basis, the correct size of
the block to be reversed.
Cheers,
Bill
>
>Wes
>
>On Tue, 2 Mar 2004, Joerg Stiller wrote:
>
>
>
>>Hello,
>>there seems to be a tradeoff between formatted and unformatted IO concerning
>>speed and portability. Do you know,
>>- what speed-up can be expected by using unformatted instead of
>>formatted read/write
>>- wether there is a standard way to convert between Big and Little
>>Endian formats?
>>
>>
>
>--
>Dr. W. J. Metzger Experimental High Energy Physics Group
>tel. +31-24-3653127 Faculty of Natural Sciences
> +31-24-3652099 (secr.) University of Nijmegen (**)
>fax. +31-24-3652191 Toernooiveld 1
> 6525 ED Nijmegen, The Netherlands
>e-mail: [log in to unmask] or [log in to unmask]
>http://home.cern.ch/metzger/ or http://www.hef.kun.nl/~wes
> (**) After 1 Sept. 2004, Radboud University Nijmegen
>
>
>------------------------------------------------------------------------
>
>#include <stdio.h>
>#include <stdlib.h>
>int main(int argc, char **argv)
>{
> FILE *input_file, *output_file;
> char *input_name, *output_name;
> unsigned int my_word;
>
> if (argc < 3)
> {
> printf("Not enough arguments!\n");
> printf("Usage: input output \n");
> exit(0);
> }
> else if (argc > 3)
> {
> printf("Too many arguments!\n");
> printf("Usage: input output \n");
> exit(0);
> }
>
> input_name = argv[1];
> output_name = argv[2];
>
> input_file = fopen( input_name,"r");
> output_file = fopen(output_name,"w");
>
> while (feof(input_file) == 0)
> {
> char *b;
> char temp;
> my_word = getw(input_file);
> if (feof(input_file) == 0)
> {
>/* printf ("%x ",my_word);*/
> /* 0xabcd -> 0xdcba */
> b = (char *) &my_word;
> temp = b[0];
> b[0] = b[3];
> b[3] = temp;
> temp = b[1];
> b[1] = b[2];
> b[2] = temp;
>/* printf ("%x \n",my_word);*/
>
> putw(my_word, output_file);
> }
>/* else*/
>/* {*/
>/* char a = 0x0a ;*/
>/* printf ("eof\n");*/
>/* putc(a, output_file);*/
>/* }*/
> }
> fclose( input_file);
> fclose(output_file);
>}
>
>
--
Bill Long [log in to unmask]
Fortran Technical Support & voice: 651-605-9024
Bioinformatics Software Development fax: 651-605-9142
Cray Inc., 1340 Mendota Heights Rd., Mendota Heights, MN, 55120
