NoteThis little-endian-big-endian conversion feature is intended for Fortran unformatted input/output operations. It enables the development and processing of files with little-endian and big-endian data organization.
In order to use the little-endian-big-endian conversion feature, specify the numbers of the units to be used for conversion purposes by setting the F_UFMTENDIAN environment variable. Then, the READ/WRITE statements that use these unit numbers will perform relevant conversions. Other READ/WRITE statements will work in the usual way.
In the general case, the variable consists of two parts divided by a semicolon. No spaces are allowed inside the F_UFMTENDIAN value. The variable has the following syntax:
F_UFMTENDIAN=MODE | [MODE;] EXCEPTION
where:
MODE = big | little
EXCEPTION = big:ULIST | little:ULIST | ULIST
ULIST = U | ULIST,U
U
= decimal | decimal -decimal
MODE defines the current
format of the data to be processed on all of the units
in the program; it can be omitted.
The keyword little means that the data is in little-endian format and will not be converted.
This is the default.
The keyword big means that
the data is in big-endian format and will be converted.
EXCEPTION defines the list of units that are the exception to MODE. The EXCEPTION keyword little or big defines the data format for the units in the EXCEPTION list. This value overrides the MODE value for the units listed. The EXCEPTION keyword and the colon can be omitted. The default when the keyword is omitted is big.
Each list member U is a simple unit number or a range of units. The number of list members is limited to 64.
decimal is a non-negative decimal number less than 232.
The command line for the variable setting in the shell is:
Sh: export F_UFMTENDIAN=MODE;EXCEPTION
Note
The environment variable value should be enclosed in quotes if the semicolon is present.
Another Possible Environment Variable Setting
The environment variable can also have the following syntax:
F_UFMTENDIAN=u[,u] . . .
The command line for the variable setting in the shell is:
Sh: export F_UFMTENDIAN=u[,u] . . .
1. F_UFMTENDIAN=big
All input/output operations perform conversion from big-endian to little-endian on READ and from little-endian to big-endian on WRITE.
2. F_UFMTENDIAN="little;big:10,20"
or F_UFMTENDIAN=big:10,20
or F_UFMTENDIAN=10,20
In this case, only on unit numbers 10 and 20 the input/output operations perform big-little endian conversion.
3. F_UFMTENDIAN="big;little:8"
In this case, on unit number 8 no conversion operation occurs. On all other units, the input/output operations perform big-little endian conversion.
4. F_UFMTENDIAN=10-20
Define 10, 11, 12 … 19, 20 units for conversion purposes; on these units, the input/output operations perform big-little endian conversion.
5. Assume you set F_UFMTENDIAN=10,100 and run the following program.
integer*4 cc4
integer*8 cc8
integer*4 c4
integer*8 c8
c4 = 456
c8 = 789
C prepare
little endian representation of data
open(11,file='lit.tmp',form='unformatted')
write(11) c8
write(11) c4
close(11)
C prepare
big endian representation of data
open(10,file='big.tmp',form='unformatted')
write(10) c8
write(10) c4
close(10)
C read
big endian data and operate with them on
C little
endian machine
open(100,file='big.tmp',form='unformatted')
read(100) cc8
read(100) cc4
C Any
operation with data, which have been read
C .
. .
close(100)
stop
end
Now compare lit.tmp and big.tmp files with the help of the od utility.
> od -t x4 lit.tmp
0000000 00000008 00000315 00000000 00000008
0000020 00000004 000001c8 00000004
0000034
> od -t x4 big.tmp
0000000 08000000 00000000 15030000 08000000
0000020 04000000 c8010000 04000000
0000034
You can see that the byte order is different in these files.