Little and Big Endian

Endianess

Endianess is the byte order of the number in the computer's memory. The number can have any size of bits, but the most common numbers used are 32 bits (4 bytes) and 16 bits (2 bytes).

There are 2 main types of endianess:

• Little endian - used mostly in Intel machines.
• Big endian - used mostly in Motorola machines.

Little endian

Little endian number is ordered from the least significant byte (LSB) in low memory address to the most significant byte (MSB) in high memory address.

Address offset	Data
0	byte0
1	byte1
2	byte2
3	byte3

Example

The hex number 0x0D0C0B0A will be represented in memory:

Address offset	Data
0	0A
1	0B
2	0C
3	0D

Big endian

Big endian number is ordered from the most significant byte (MSB) in low memory address to the least significant byte (LSB) in high memory address.

Address offset	Data
0	byte3
1	byte2
2	byte1
3	byte0

Example

The hex number 0x0D0C0B0A will be represented in memory:

Address offset	Data
0	0D
1	0C
2	0B
3	0A

Bits order

The order of the bits inside the byte is not changed when converting from little to big or from big to little.

Bi-endianess

Many processors allow to configure the endianess type to little endian or big endian.

Endianess table

Machine / Processor	Endianess
Intel Pentium / x86 (PC)	Little
ARM	Little / Big
PowerPC	Big / Little
Motorola 68000	Big
MIPS	Big / Little
Sun Sparc	Big / Little
TI TMS320C6000	Big / Little
Analog ADMC / Sharc	Big
Java	Big
Network	Big
PC / Windows	Little
Mac / OS-X	Big / Little
Linux	Big / Little
Unix	Big / Little

Endian converter

TBD

Big / little endian conversion C code

The conversion is done, simply by swapping the bytes in memory for a 32 bit number.

Byte0 is swapped with byte3. Byte1 is swapped with byte2.

The conversion works both ways - from big to little and from little to big.

32 bits endian conversion of long number

unsigned long EndianSwap32(unsgined long x)

{

    unsigned long y=0;

    y += (x & 0x000000FF)<<24

    y += (x & 0xFF000000)>>24

    y += (x & 0x0000FF00)<<8

    y += (x & 0x00FF0000)>>8

    return x

}

32 bits endian conversion of char array

void EndianSwap32(unsgined char c[])

{

    unsigned char tmp;

    tmp  = c[0];

    c[0] = c[3];

    c[3] = tmp;

    tmp  = c[1];

    c[1] = c[2];

    c[2] = tmp;

}

CPU endianess check C code

Here is a C code function to finds the endianess of the CPU:

typedef enum _endian {little_endian, big_endian} EndianType;

 

EndianType CheckCPUEndian()

{

    unsigned short x;

    unsigned char c;

    EndianType CPUEndian;

 

    x = 0x0001;;

    c = *(unsigned char *)(&x);

    if( c == 0x01 )

        CPUEndian = little_endian;

    else

        CPUEndian = big_endian;

 

    return CPUEndian;

}

 

---

See also

• RGB color
• C Reference
• Endianess - Wikipedia