Byte Ordering on Big Endian and Little Endian Platforms

Definitions

Integer values are typically stored in one of three sizes: one-byte, two-byte, or four-byte. The ordering of the bytes for the integer varies depending on the platform (operating environment) on which the integers were produced.

The ordering of bytes differs between the "big endian" and the "little endian" platforms. These colloquial terms are used to describe byte ordering for IBM mainframes (big endian) and for Intel-based platforms (little endian). In the SAS System, the following platforms are considered big endian: IBM mainframe, HP-UX, AIX, Solaris, and Macintosh. The following platforms are considered little endian: VAX/VMS, AXP/VMS, Digital UNIX, Intel ABI, OS/2, and Windows.

How the Bytes are Ordered

On big endian platforms, the value 1 is stored in binary and is represented here in hexadecimal notation. One byte is stored as 01, two bytes as 00 01, and four bytes as 00 00 00 01. On little endian platforms, the value 1 is stored in one byte as 01 (the same as big endian), in two bytes as 01 00, and in four bytes as 01 00 00 00.

If an integer is negative, the "two's complement" representation is used. The high-order bit of the most significant byte of the integer will be set on. For example, -2 would be represented in one, two, and four bytes on big endian platforms as FE, FF FE, and FF FF FF FE respectively. On little endian platforms, the representation would be FE, FE FF, and FE FF FF FF.

Reading Data Generated on Big Endian or Little Endian Platforms

SAS can read signed and unsigned integers regardless of whether they were generated on a big endian or a little endian system. Likewise, SAS can write signed and unsigned integers in both big endian and little endian format. The length of these integers can be up to eight bytes.

The following table shows which informat to use for various combinations of platforms. In the Sign? column, "no" indicates that the number is unsigned and cannot be negative. "Yes" indicates that the number can be either negative or positive.

SAS Informats and Byte Ordering
Data created for ... Data read on ... Sign? Informat

big endian big endian yes IB or S370FIB

big endian big endian no PIB, S370FPIB, S370FIBU

big endian little endian yes IBR

big endian little endian no PIBR

little endian big endian yes IBR

little endian big endian no PIBR

little endian little endian yes IB or IBR

little endian little endian no PIB or PIBR

big endian either yes S370FIB

big endian either no S370FPIB

little endian either yes IBR

little endian either no PIBR

***SAS Informats and Byte Ordering***
Data created for ...	Data read on ...	Sign?	Informat
big endian	big endian	yes	IB or S370FIB
big endian	big endian	no	PIB, S370FPIB, S370FIBU
big endian	little endian	yes	IBR
big endian	little endian	no	PIBR
little endian	big endian	yes	IBR
little endian	big endian	no	PIBR
little endian	little endian	yes	IB or IBR
little endian	little endian	no	PIB or PIBR
big endian	either	yes	S370FIB
big endian	either	no	S370FPIB
little endian	either	yes	IBR
little endian	either	no	PIBR

Integer Binary Notation in Different Programming Languages

The following table compares integer binary notation according to programming language.

Integer Binary Notation and Programming Languages
Language 2 Bytes 4 Bytes

SAS IB2., IBR2., PIB2.,PIBR2., S370FIB2., S370FIBU2., S370FPIB2. IB4., IBR4., PIB4., PIBR4., S370FIB4., S370FIBU4., S370FPIB4.

PL/I FIXED BIN(15) FIXED BIN(31)

FORTRAN INTEGER*2 INTEGER*4

COBOL COMP PIC 9(4) COMP PIC 9(8)

IBM assembler H F

C short long

***Integer Binary Notation and Programming Languages***
Language	2 Bytes	4 Bytes
SAS	IB2., IBR2., PIB2.,PIBR2., S370FIB2., S370FIBU2., S370FPIB2.	IB4., IBR4., PIB4., PIBR4., S370FIB4., S370FIBU4., S370FPIB4.
PL/I	FIXED BIN(15)	FIXED BIN(31)
FORTRAN	INTEGER*2	INTEGER*4
COBOL	COMP PIC 9(4)	COMP PIC 9(8)
IBM assembler	H	F
C	short	long

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