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Questions tagged [endianness]

Endianness refers to how multi-byte values are stored in memory, sent between devices or stored on disk. "Big-Endian" values are stored with their most-significant byte first, and "Little-Endian" values are stored with their least-significant byte first. Other byte-orders are possible but very uncommon, and cannot be described this way.

Endianness is the organization and ordering of byte values in multi-byte words. There are two main forms of endianness: big-endian and little-endian.

Big endian (BE) means that the most significant bits are stored first (lowest address). It is similar to reading or saying the name of a decimal number in reading order.

Little endian (LE) means that the least significant bits are stored first. The bytes are stored in reverse of the big-endian format.

There are other forms of byte orderings, but they are rare. They may also be called mixed-endian.

Usage of endianness

When we talk about endian, we often refer to the endianness of an instruction architecture/CPU or the endianness of a file. The endianness of an architecture or a CPU is how the processor organizes the bits in a multi-byte word.

  • Motorola 68000 is a big-endian architecture. It stores multi-byte words in big-endian ordering.
  • Intel processors and the x86 architecture are little-endian.
  • MIPS can run in both big-endian and little-endian format, and you can select the endianness. MIPS is a Bi-endian format.

The endianness of a file indicates how the bytes of a multi-byte word is ordered in a given file (applies both to binary and text files). Sometimes, we indicate the endianness of a file by putting a byte-order mark (BOM) as the first byte of that file.

  • A big-endian UTF-16 text file with BOM would begin with the two bytes FE FF and have all the two-byte characters (each surrogate in a surrogate pair is also one character) be expressed in big endian.
  • A little-endian UTF-16 text file with BOM would begin with the two bytes FF FE and have all the two-byte characters be expressed in little endian.

Examples of endianness

A 32-bit signed int value, 12356789 is stored as four bytes in two's complement format.

  • In big endian, the value is stored as 07 5B CD 15 in hexadecimal notation.
  • In little endian, the value is stored as 15 CD 58 07 in hexadecmial notation.

A UTF-16 text file with BOM contains these characters: A 汉.

  • The BOM character has value U+FEFF. The emoji has Unicode value U+1F197 is expressed as two surrogate pairs, U+D83C U+DD97
  • In big endian, the characters are stored as FEFF 0041 0020 6C49 D83C DD97
  • In little endian, they are stored as FFFE 4100 2000 496C 3CD8 97DD

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How to prepend a 2-byte string size and send it over TCP

I have an application which sends received UDP packets over TCP connection. I'm storing the UDP packet data in a std::string object. For TCP send/receive, I'm using a data encoding/decoding scheme as <2-byte data length>. This is my…
RishiN
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Memory reading time

I heard that reading one byte from non-cached memory can take up to 50 CPU cycles. So, does reading int from memory take 4 times as long as reading char, meaning up to 200 cycles? If not, is it a good idea to get 4-8 chars at a time with *(size_t…
beardeadclown
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Use Python Construct to parse 64b *little* endian bitmap into an array of bytes

I need to parse a 64 bit little endian memory into an array of 64 bytes. One bit parses to 1 byte. This will allow me later on to use those bytes for further parsing. Example: 3B 94 00 00 00 00 00 00 Should be parsed into: 1001010000111011. The 1011…
YL_embedded
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Ruby network byte order to native endianness from array of byte values

Say I have an array like this arr = [24, 21, 25, 40, 236, 89] which is meant to represent an IP address (first four bytes) and a port number (last 2 bytes), as in http://wiki.theory.org/BitTorrentSpecification#Tracker_Response, the binary peer…
HRÓÐÓLFR
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How numbers saved in memory?

I am quit not sure about this problem for a long time and want some help. Given the following 2 - bytes number y which is equal to: 0x0110, that's declared in assembly in data section, how is it stored in memory? In little endian lower bytes are…
user15982858
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Correct reading of samples from .wav file

I am trying to read correctly a WAVE file, PCM, mono, 16 bits (2 bytes per sample). I have managed to read the header. The problem is reading (writing) the data part. As far as I understand the 16-bit samples in the data chunk are little-endian, and…
Barsaas
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Endianes confusion in load word/store word (MIPS/QtSpim)

Cheers, so I am a little confused with the whole endianess things, and as I thought I had it figured out I cam across an example and completely lost it. So the code is as follows: .text .globl __start __start: lw $t7, stringInWordForm …
george.zrs
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array of bytes to num

I have for example tab = [0x51, 0x3c, 0xb8, 0x15] then I want to convert this table to integer 0x15b83c51 = 363323840 any ideas?
basher
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Why Binary numbers in little endian machine was saved as this?

Like this case: 0x01234567, When it's in big endian machine , it was saved as [01][23][45][67].That's clear and understanderable; But when it's in little endian machine , it was saved as [67][45][23][01].That's the thing casusing my confusion. Why…
Seight
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Numpy pack bits into 32-bit little-endian values

Numpy provides packbits function to convert from values to individual bits. With bitorder='little' I can read them in C as uint8_t values without issues. However, I would like to read them as uint32_t values. This means that I have to reverse the…
Curious
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To big endian or to little endian?

let's say that we ignore the target and source hardware for a moment. So, what's the better endian style to go with -- big or small? I'm just trying to go with consensus / convention on this one. The best guidance I've received so far is "it…
sgtz
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Adding a 32-bit wrong-endian number in x86 asm

I'm rolling off my own TCP/IP stack. The network byte ordering is different from the PC byte ordering, and I see this when I run tests on my own stack with linux tcpdump. If I take a 16-bit network value and I want to increment the original value by…
Mike St
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Can I use union to convert between integers of various size?

Let's consider a union of integers of different sizes. Is it guaranteed that if a number fits the range of each of the integer types, it can be written to and read out from any of the union data members correctly? E.g. this code union U { …
user1079505
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What is the correct way to read this file in python?

I am trying to parse a binary file that contains a dump of network packets. The specification for the network packets says that it follows the Big Endian format. Following is a snippet from the file 0400 0001 004f 1a04 595a 2a2a 3132 3300 4000 054d…
valitor1990
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How C read 4 bytes numbers due to endianess?

If i write the following code in C: int n; n = 2864434397; int i; i = &n; //I know there will be a warning, it's ok due to the little endian convention the variable n, on my stack, will be, for example: 0xffffd12c: 0xdd 0xffffd12d: 0xcc…
Q Stack
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