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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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Is there any conversions when storing/reading integers of different size to/from union?

Reading Rapidjson code I found some interesting optimization with "type punning". // By using proper binary layout, retrieval of different integer types do not need conversions. union Number { #if RAPIDJSON_ENDIAN == RAPIDJSON_LITTLEENDIAN …
kyb
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trying to format hex into little endian in c

So I'm trying to get the sum of the values in a buffer, however, the values need to be rearranged in order to do so. Essentially how do I get C to convert the values in this array:uint16_t inp[] = {0xFF,0x81,0xFD,0x00,0x00,0x00,0x00,0x08,0x00,0x00};…
rob ell
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assembly data addressing how does little endian work?

.data x dw 7A6H, 30B0H y db 20H z dw 1, 2, 3 .code mov ax, @data mov ds, ax lea si, y mov bl, [si+2] The value of the register bl is 0, why is that? Shouldn't it be 2 from the z dw array?
Mostfa shma
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Hexadecimal representation on little and big endian systems

Consider the following code : unsigned char byte = 0x01; In C/C++ the hexadecimal will be considered as an int, and therefore will be expanded to more then one byte. Because there is more then one byte, if the system uses little or big endian has…
rrrrTTTrrrr
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DPDK changes pakcets content when sending out packets through `rte_eth_tx_burst`

I construct DPDK packets with following code: #define PKG_GEN_COUNT 1 #define EIU_HEADER_LEN 42 #define ETHERNET_HEADER_LEN 14 #define IP_DEFTTL 64 /* from RFC 1340. */ #define IP_VERSION 0x40 #define IP_HDRLEN 0x05 /* default IP header length ==…
Hovin
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Is there a way to copy_from_slice with a dynamic size?

I am attempting to change an unknown section of a Vec into a 32 bit integer using from_le_bytes. I know that the size will be between 1 and 4 bytes, but that's all I know. Here is my attempt: use std::u32; fn main () { let my_vec : Vec =…
VCD_WL
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Reversing the bitwise endianness of a number

Is there a standard library way in python to get the equivalent of a number reading bits in reverse ? (Apart from converting to a string, reversing it, and converting back) Example of expected behavior : >>> reverse(20) # 20 = b10100 5 # 5 =…
ice-wind
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Python struct.unpack byte length issues

I have the following code: msg = b'0,[\x00\x01\x86\xec\x96N' print(struct.unpack("<"+"I",msg)) however everytime i try to do this it says struct.error: unpack requires a buffer of 4 bytes What i tried to do is the following times = int(len(msg)/4) …
Marcus F
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Converting strings into little endian bytes in Swift?

Perhaps I'm a little too new to understanding little endian, but I am trying to achieve a task that seems to be confusing me. I am working with point clouds in my iOS app, and am trying to pragmatically create a PLY file for export. The app is…
ZbadhabitZ
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shell: convert decimal to native hex number

I have a trivial C program below which takes an int as input and dumps the memory layout to the terminal: # cat foo.c #include #include int main(int argc, char **argv) { int i, foo = atoi(argv[argc-1]); unsigned char…
jblerks
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Converting big endian bytes into integer?

I have this python code: f = open('file.bin', 'rb') b = f.read(2) bytes = b[0x0:0x2] //this is b'\x10\x24', for example f.close() a = int.from_bytes(bytes, 'big') //returns 4132 I can't seem to figure out how to achieve the same thing in C#. Did…
ZeroSkill
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Why does memcpy() handle integer destination as Big Endian but does not for char destination?

The computer I am running the following code is Little Endian. uint32_t src_uint = 0xAABBCCDD; uint32_t dest_uint = 0; uint8_t dest_arr[4] = {0}; memcpy(&dest_uint, &src_uint, 4); printf("\ndest_uint: 0x%X\n", dest_uint); // output:…
Rafael Nagel
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Why does assigning a hex value give big-endian equivalent value on a little-endian machine?

Here is a simple c statement: uint32_t x = 0x04000000; On my little endian machine I assumed x would equal 4. But instead it's 67108864. So there must be something very basic that I don't understand. Could you help explain please?
Adham Zahran
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Explaining (lack of) endianness as it applies to a string

For this question, I'm going to assume every character is single-byte ascii. If my understanding is correct, endianness applies to the byte-ordering of multi-byte words. Because strings only have one byte per character there is no endianness. But…
carl.hiass
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How can a Mac read a binary data file created by an old SGI (680x0 Motorola CPU)?

In a Mac (thus, 64 bit, little endian), I want to read a binary data file, created in a ~1989 SGI (Irix 3.x, 680x0 Motorola CPU, thus, 32 bit, big endian). Data in that file was written using the C code: …
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