Seeing as we are starting to attract quite the coding crowd and @FaunCB happens to be a very big risc and power pc architecture fan where I am a very heavy x86 enthusiast oh and ARM (which is risc) aight i guess to… RISC and CISC have their advantages and disadvantages and none is better then the other
Perhaps its time to provide a solid reference that people can link to when people find themselves asking what the heck is this endian stuff ? something outta minecraft XD?
Lets take a look at my notes shall we?
What are the two different theories, what do they set out to accomplish?
Little Endian and Big endian are two ways of storing multi-byte data-types ( int, float, etc) in computers. In a sense this is how the computer stores data in its processor registers, which can hold a variety of data types from instructions to storage addresses to stack pointers.
What’s the difference between the theories?
In Little Endian machines, last byte or least significant bit of binary representation of the multi-byte data-type is stored first while in Big Endian machines, first byte or most significant bit of binary representation of the multi-byte data-type is stored first.
For example:
Suppose an integer is stored as 4 bytes(32-bits), then a variable y with value 0xdeadbeef( Hexa-decimal representation) is stored as four bytes 0xDE, 0xAD, 0xBE, 0xEF, on Big-endian while on Little-Endian (Intel x86), it will be stored in reverse order as follows 0xEF 0xBE 0xAD 0xDE.
Example: How 0x1234567 is stored at memory location 0x100-ox103 on any standard machine at home?
Here is a piece of code from my ECE330 class that I wrote to do exactly that for a test given zero help to test endianness the third day of class. Execute it at home on a linux machine prefereably with all the build tools LOL… Or windows whichever you may prefer the operating system is completely irrelevant
#include <stdio.h>
/* function to show bytes in memory, from location start to start+n*/
void show_mem_rep(char *start, int n){
int i;
for (i = 0; i < n; i++)
printf(" %.2x", start[i]);
printf("\n");
}
/*Main function to call above function for 0xba5eba11*/
int main(){
int i = 0xba5eba11;
show_mem_rep((char *)&i, sizeof(i));
return 0;
}
How to remember?
Well think about this. If you have two fishes. In big endian you have the whole fish but lets try to think about it as two halves of the fish in the correct order. representing each bit. Now in little endian you cut the fish in half and put the tail first then start counting. See the difference? Draw it for yourself all you gotta remember is that in Little Endian, things are stored in reverse order.
So you find yourself asking which is better?
Both have advantages and disadvantages:
In “Little Endian” form, assembly language instructions for picking up a 1, 2, 4, or longer byte number proceed in exactly the same way for all data storage formats. The process goes like this… first pick up the lowest order byte at offset 0. Also, because of the 1:1 relationship between address offset and byte number (offset 0 is byte 0), multiple precision math routines are correspondingly easier to write. Armed with that knowledge we can see why we write most mathematical routines in little endian.
In “Big Endian” form, by having the high-order byte come first, you can always test whether the number is positive or negative by looking at the byte at offset zero which is incredibly useful because you don’t have to know how long the number is, nor do you have to skip over any bytes to find the byte containing the sign information of the data or numerical instruction set. The numbers are also stored in the order in which they are printed out, so binary to decimal routines are particularly efficient and easier to read by humans
So what software has what kind of endianess?
Glad you asked…
Adobe Photoshop – Big Endian
BMP (Windows and OS/2 Bitmaps) – Little Endian
DXF (AutoCad) – Variable
GIF – Little Endian
IMG (GEM Raster) – Big Endian
JPEG – Big Endian
FLI (Autodesk Animator) – Little Endian
MacPaint – Big Endian
PCX (PC Paintbrush) – Little Endian
PostScript – Not Applicable (text!)
POV (Persistence of Vision ray-tracer) – Not Applicable (text!)
QTM (Quicktime Movies) – Little Endian (on a Mac!)
Microsoft RIFF (.WAV & .AVI) – Both
Microsoft RTF (Rich Text Format) – Little Endian
SGI (Silicon Graphics) – Big Endian
Sun Raster – Big Endian
TGA (Targa) – Little Endian
TIFF – Both, Endian identifier encoded into file
WPG (WordPerfect Graphics Metafile) – Big Endian (on a PC!)
XWD (X Window Dump) – Both, Endian identifier encoded into file
And so on
If you ever find yourself in need of reversing the order of a multibyte integer to suit your liking… there are many methods to doing so
It is pretty easy to reverse a multibyte integer if you find you need the other format. A single function can be used to switch from one to the other, in either direction. A simple and not very efficient version might look as follows:
Function Reverse (N:LongInt) : LongInt ;
Var B0, B1, B2, B3 : Byte ;
Begin
B0 := N Mod 256 ;
N := N Div 256 ;
B1 := N Mod 256 ;
N := N Div 256 ;
B2 := N Mod 256 ;
N := N Div 256 ;
B3 := N Mod 256 ;
Reverse := (((B0 * 256 + B1) * 256 + B2) * 256 + B3) ;
End ;
A more efficient version that depends on the presence of hexadecimal numbers, bit masking operators AND, OR, and NOT, and shift operators SHL and SHR might look as follows:
Function Reverse (N:LongInt) : LongInt ;
Var B0, B1, B2, B3 : Byte ;
Begin
B0 := (N AND $000000FF) SHR 0 ;
B1 := (N AND $0000FF00) SHR 8 ;
B2 := (N AND $00FF0000) SHR 16 ;
B3 := (N AND $FF000000) SHR 24 ;
Reverse := (B0 SHL 24) OR (B1 SHL 16) OR (B2 SHL 8) OR (B3 SHL 0) ;
End ;
There are certainly more efficient methods, some of which are quite machine and platform dependent as @FaunCB pointed out the Power Architecture has its own way of doing so that is optimized for its platform… Use what works best for your situation
@wendell feel free to chime in if I left some important bits out (no pun intended). Bound to have made some mistakes somewhere.
for those wishing to learn more:
https://betterexplained.com/articles/understanding-big-and-little-endian-byte-order/
You may link to this explanation anywhere you see fit on the forum and or post a link to it to explain the difference if you ever find yourself in the need of explaining it or talking about endianess in your post
