All information in computers is stored in the form of bits, where each bit can be either a 0 or a 1. Most modern computers use as the unit of memory a byte, which consists of eight bits and which can contain 256 different values. LUX’s data types (Numerical Data Types) all consist of an integral number of bytes. If a data value consists of more than one byte, then the byte that counts the smallest units of the value is called the least significant byte and the byte that counts the biggest units of the value is called the most significant byte. The bytes of a multi-byte data value can be stored in memory in different orders. The two byte orders used the most are the one in ascending order of significance, often referred to as little-endian (because you start at the end of the "little" values), and the one in descending order of significance, often called bigendian.
What happens if you try to read data on a bigendian machine that was
written on a littleendian one? If you use any of the classical file I/O
operations (i.e., following
openu), or use direct
mapping of an array structure onto a disk file (i.e.,
fltfarr and its cousins), then LUX cannot automatically correct
for the byte order discrepancy, because arbitrary files do not contain
indications of how many bytes make up a value, and what their byte order
might be. However, LUX provides the routine
switches the byte order of the data in a variable from littleendian to
bigendian or the other way around, so in this case you can read the data
as usual and then switch its byte order if necessary.
If you use files that conform to LUX’s own FZ format (written using,
store) then the data’s
type and byte order are included in the file’s header so any necessary
corrections for byte order discrepancies are taken care of
automatically. If you create such a file, then the data is always
written in your machine’s native byte order.
fzarr function which assigns an array structure to an FZ disk
file does not correct for byte order discrepancies, even though the FZ
file contains byte order information. This is because
returns an appropriate file array (File Arrays) to access the file
data and file arrays do not contain byte order information. This means
that if you copy a file from a bigendian machine to a littleendian
machine, or the other way around, then you cannot use a file array to
access that data (except if you combine such access with the use of
To find out if your computer is bigendian or littleendian, you can check
the value of read-only global variable
#msbfirst: if it is equal
1, then the most significant byte comes first (i.e., your
computer is bigendian), and if it is equal to
0, then the least
significant byte comes first (it is littleendian).
Another way is to execute
t,bmap(1). If the result is
0 1, then your computer is bigendian; if the result is
1 0 0 0
then your computer is littleendian.
See also: Disk File I/O, #msbfirst