help mata byteorder()
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Title
[M-5] byteorder() -- Byte order used by computer
Syntax
real scalar byteorder()
Description
byteorder() returns 1 if the computer is HILO (records most significant
byte first) and returns 2 if LOHI (records least significant byte first).
Remarks
Pretend that the values 00 and 01 are recorded at memory positions 58 and
59 and that you know what is recorded there is a 2-byte integer. How
should the 2-byte number be interpreted: as 0001 (meaning 1) or 0100
(meaning 256 in decimal)? For different computers, the answer varies.
For HILO computers, the number is to be interpreted as 0001. For LOHI
computers, the number is interpreted as 0100.
Regardless, it does not matter because the computer is consistent with
itself. An issue arises, however, when we write binary files that may be
read on computers using a different byte order or when we read files from
computers that used a different byte order.
Stata and Mata automatically handle these problems for you, so you may
wish to stop reading. byteorder(), however, is the tool on which the
solution is based. If you intend to write code based on your own
binary-file format or to write code to process the binary files of
others, then you may need to use it.
There are two popular solutions to the byte-order problem: (1) write the
file in a known byte order or (2) write the file by using whichever byte
order is convenient and record the byte order used in the file.
StataCorp tends to use the second, but others who have worried about this
problem have used both solutions.
In solution (1), it is usually agreed that the file will be written in
HILO order. If you are using a HILO computer, you write and read files
the ordinary way, ignoring the problem altogether. If you are on a LOHI
computer, however, you must reverse the bytes before placing them in the
file. If you are writing code designed to execute on both kinds of
computers, you must write code for both circumstances, and you must
consider the problem when both reading and writing the files.
In solution (2), files are written LOHI or HILO, depending solely on the
computer being used. Early in the file, however, the byte order is
recorded. When reading the file, you compare the order in which the file
is recorded with the order of the computer and, if they are different,
you reverse bytes.
Mata-buffered I/O utilities will automatically reverse bytes for you.
See [M-5] bufio().
Conformability
byteorder():
result: 1 x 1
Diagnostics
None.
Source code
Function is built in.
Also see
Manual: [M-5] byteorder()
Help: [M-5] bufio(); [M-5] stataversion(); [M-4] programming
