Endianness
ALIAS: big-endian, little-endian
Byte orders
Endianness is primarily expressed as:
- big-endian (BE): the most significant byte of a word are stored at the smallest memory address and the least significant byte at the largest
- Also known as the network byte order or network order
- little-endian (LE): the least-significant byte are stored at the smallest address
A 4-byte integer 0x12345678 (305419896 decimal) would be ordered natively (arranged in and handled by the CPU registers) into bytes as
- 0x12 0x34 0x56 0x78 for big-endian
- 0x78 0x56 0x34 0x12 for little-endian
Some systems may have even weirder byte orders called mid-endian, middle-endian, mixed-endian, or just weird.
- 0x56 0x78 0x12 0x34
- 0x34 0x12 0x78 0x56
Perl
pack & unpack
The integer formats s, S, i, I, l, L, j, and J are inherently non-portable between processors and operating systems because they obey native byteorder and endianness.
For portably packed integers, either use the formats n, N, v, and V or else use the > and < modifiers.
Storable
The Storable package brings persistence to Perl data structures containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be conveniently stored to disk and retrieved at a later time.
Use nstore for storing data in network order to allow easy sharing across multiple platforms, or when storing on a socket known to be remotely connected. At retrieval time, data will be correctly restored without knowing whether you’re restoring from native or network ordered data. Double values are stored stringified to ensure portability as well, at the slight risk of loosing some precision in the last decimals.
Determine your system endianness
Run this incantation
$ perl -e 'printf("%#02x ", $_) for unpack("W*", pack L=>0x12345678);'
0x78 0x56 0x34 0x12 # little-endian
Get the byteorder on the platform where Perl was built:
use Config;
print "$Config{byteorder}\n";
and from the command line:
perl -V:byteorder
Byteorders “1234” and “12345678” are little-endian Byteorders “4321” and “87654321” are big-endian
Systems with multiarchitecture binaries will have “ffff” , signifying that static information doesn’t work, one must use runtime probing.
Origin
The names big-endian and little-endian are comic references to the egg-eating habits of the little-endian Lilliputians and the big-endian Blefuscudians from the classic Jonathan Swift satire, Gulliver’s Travels.
This entered computer lingo via the paper “On Holy Wars and a Plea for Peace” by Danny Cohen, USC/ISI IEN 137, April 1, 1980.
Lilliput and Blefuscu
Lilliput and Blefuscu are two fictional island nations that appear in the first part of the 1726 novel Gulliver’s Travels by Jonathan Swift.
The novel further describes an intra-Lilliputian quarrel over the practice of breaking eggs. Traditionally, Lilliputians broke boiled eggs on the larger end; a few generations ago, an Emperor of Lilliput, the Present Emperor’s great-grandfather, had decreed that all eggs be broken on the smaller end after his son cut himself breaking the egg on the larger end. The differences between Big-Endians (those who broke their eggs at the larger end) and Little-Endians had given rise to “six rebellions … wherein one Emperor lost his life, and another his crown”. The Lilliputian religion says an egg should be broken on the convenient end, which is now interpreted by the Lilliputians as the smaller end. The Big-Endians gained favour in Blefuscu.
English Catholicism and Protestantism
The Big-Endian/Little-Endian controversy reflects, in a much simplified form, British quarrels over religion. Less than 200 years previously, England had been a Catholic (Big-Endian) country; but a series of reforms beginning in the 1530s under King Henry VIII (reigned 1509–1547), Edward VI (1547–1553), and Queen Elizabeth I (1558–1603) had converted most of the country to Protestantism (Little-Endianism), in the episcopalian form of the Church of England. At the same time, revolution and reform in Scotland (1560) had also converted that country to Presbyterian Protestantism, which led to fresh difficulties when England and Scotland were united under one ruler, James I (1603–1625).