littleEndian/bigEndian

[docschnipp]

Hi,

as someone pulling to C# over from C++ I stumbled over something today for
which I was not able to find an answer:

HOW do I convert a byte block with a given endianess to an int32 and vice
versa?

In C++ I have this:

#pragma intrinsic(_byte swap_ushort)
#pragma intrinsic(_byte swap_ulong)

*myword = _byteswap_ulong (mybigendianwor d);

which results in a wonderful single assembler instruction.

The only documentation I found about endianess is on handling UTF8/16
strings, but not with binary stuff.

Can someone give me a hint how I perform such things FAST and not via my own
clumsy version?

thanks
doc

[Jon Skeet [C# MVP]]

docschnipp wrote:

as someone pulling to C# over from C++ I stumbled over something today for
which I was not able to find an answer:

HOW do I convert a byte block with a given endianess to an int32 and vice
versa?

Have a look at http://www.pobox.com/~skeet/csharp/miscutil
In particular, the EndianBinaryRea der/Writer and EndianBitConver ter.

Jon

[docschnipp]

"Jon Skeet [C# MVP]" wrote:

docschnipp wrote:

as someone pulling to C# over from C++ I stumbled over something today for
which I was not able to find an answer:

HOW do I convert a byte block with a given endianess to an int32 and vice
versa?

Have a look at http://www.pobox.com/~skeet/csharp/miscutil
In particular, the EndianBinaryRea der/Writer and EndianBitConver ter.

"Every so often, someone on the newsgroup asks about something which doesn't
exist in the framework, but which I think should. Sometimes, I'll write some
code for them to plug the gap. "

Well, fits perfect I guess :)

I'll take a look into it, thanks.

doc

[GhostInAK]

Hello docschnipp,

Here's what I currently use (in VB):

Public Function ReadBigEndianIn t32() As Int32

Dim tReturn As Int32 = 0
Dim tBuffer(3) As Byte

oStream.Read(tB uffer, 0, tBuffer.Length)

Array.Reverse(t Buffer)
tReturn = BitConverter.To Int32(tBuffer, 0)

Return tReturn

End Function

And the inverse of course for Writing..

-Boo

Hi,

as someone pulling to C# over from C++ I stumbled over something today
for which I was not able to find an answer:

HOW do I convert a byte block with a given endianess to an int32 and
vice versa?

In C++ I have this:

#pragma intrinsic(_byte swap_ushort)
#pragma intrinsic(_byte swap_ulong)
*myword = _byteswap_ulong (mybigendianwor d);

which results in a wonderful single assembler instruction.

The only documentation I found about endianess is on handling UTF8/16
strings, but not with binary stuff.

Can someone give me a hint how I perform such things FAST and not via
my own clumsy version?

thanks
doc

[Jon Skeet [C# MVP]]

GhostInAK <gh*******@gmai l.com> wrote:

Here's what I currently use (in VB):

Public Function ReadBigEndianIn t32() As Int32

Dim tReturn As Int32 = 0
Dim tBuffer(3) As Byte

oStream.Read(tB uffer, 0, tBuffer.Length)

Array.Reverse(t Buffer)
tReturn = BitConverter.To Int32(tBuffer, 0)

Return tReturn

End Function

That's not guaranteed to work - calling Read on a stream isn't
guaranteed to read all the bytes you ask for. It's likely to, but it's
not guaranteed.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
If replying to the group, please do not mail me too

[Claes Bergefall]

IPAddress.Netwo rkToHostOrder
IPAddress.HostT oNetworkOrder

(not sure why these are in the IPAddress class but they're static anyway)

/claes

"docschnipp " <do********@new sgroup.nospam> wrote in message
news:BC******** *************** ***********@mic rosoft.com...

Hi,

as someone pulling to C# over from C++ I stumbled over something today for
which I was not able to find an answer:

HOW do I convert a byte block with a given endianess to an int32 and vice
versa?

In C++ I have this:

#pragma intrinsic(_byte swap_ushort)
#pragma intrinsic(_byte swap_ulong)

*myword = _byteswap_ulong (mybigendianwor d);

which results in a wonderful single assembler instruction.

The only documentation I found about endianess is on handling UTF8/16
strings, but not with binary stuff.

Can someone give me a hint how I perform such things FAST and not via my
own
clumsy version?

thanks
doc

[GhostInAK]

Hello Jon Skeet [C# MVP],

Jon,

Thanks for the comment. I became aware of that fact the other day and just
hadn't got around to updating the routine at the time of the post.

Thanks,
-Boo

GhostInAK <gh*******@gmai l.com> wrote:

Here's what I currently use (in VB):

Public Function ReadBigEndianIn t32() As Int32

Dim tReturn As Int32 = 0
Dim tBuffer(3) As Byte
oStream.Read(tB uffer, 0, tBuffer.Length)

Array.Reverse(t Buffer)
tReturn = BitConverter.To Int32(tBuffer, 0)
Return tReturn

End Function

That's not guaranteed to work - calling Read on a stream isn't
guaranteed to read all the bytes you ask for. It's likely to, but it's
not guaranteed.

[docschnipp]

"Claes Bergefall" wrote:

IPAddress.Netwo rkToHostOrder
IPAddress.HostT oNetworkOrder

(not sure why these are in the IPAddress class but they're static anyway)

/claes

Usually because the libs connected to sockets, tcp/ip etc. are early cross
platform libs and need all the translation of network to local endianess.

I now decided to use this variant until I find something better:

----------
UInt32 myBigEndian = 0xdeadbeef;
UInt32 mLittleEndian = ( (myBigEndian& 0xFF000000) >> 24) | ((myBigEndian&
0x00FF0000) >>8) | (( myBigEndian& 0x0000FF00) <<8 ) | ((myBigEndian&
0x000000FF) << 24);
----------

The big advantage is: it works for all scales of integers and is not too
clumsy. Unfortunately I found no source for something that allows the native
compiler to take use of the bswap mnemonic. I would really appreciate a way
to make this very fast. bswap takes 2 ( 1 cycle plus prefix ) cycles only,
the code above ~34 cycles.

I have to read a _lot_ of data, several dozends of megabytes so
investigation on this topic is a worthwhile goal for me.
thanks for input,

doc

[docschnipp]

Hi Guys,

I've made some tests, the Reverse() method seems to be the slowest of all.

The code is found below, results were:

Time 1: 3765 ( the .Reverse/BitConverter method )
Time 2: 1322 ( the manual reindexing/BitConverter method )
Time 3: 1071 ( the Bitconverter/reshift method )
(if UInt is not needed, only Int:)
Time 4: 191 ( the shift the bytes directly/OR method )
So I think I will stick to method 3 and 4. Does anyone knows how I can cast
a byte to uint? :)

Thanks for all your input.

UInt32 mLittleEndian;
int loopcount = 20000000;

s1 = Environment.Tic kCount;
Array.Copy(myOr g,0,myArr,0,4);
for (i = 0; i < loopcount; i++)
{
if ( BitConverter.Is LittleEndian )
{
Array.Reverse(m yNew,0,4);
}
mLittleEndian = BitConverter.To UInt32(myNew,0) ;
}
s2 = Environment.Tic kCount;
Array.Copy(myOr g,0,myArr,0,4);
for ( i = 0; i< loopcount ; i++)
{
if ( BitConverter.Is LittleEndian )
{

myNew[3] = myArr[0];
myNew[2] = myArr[1];
myNew[1] = myArr[2];
myNew[0] = myArr[3];
mLittleEndian = BitConverter.To UInt32(myNew,0) ;
}
}
s3 = Environment.Tic kCount;

// UInt32 mLittleEndian;
for ( i = 0; i< loopcount ; i++)
{
// myBigEndian = BitConverter.To UInt32(myNew,0) ;
myBigEndian = BitConverter.To UInt32(myOrg,0) ;
if ( BitConverter.Is LittleEndian)
{
mLittleEndian = ( (myBigEndian & 0xFF000000) >24) |
((myBigEndian & 0x00FF0000) >>8) | (( myBigEndian &
0x0000FF00) <<8 ) | ((myBigEndian & 0x000000FF) << 24);
}
}
s4 = Environment.Tic kCount;
Int32 mSLittleEndian;
for ( i = 0; i< loopcount ; i++)
{
if ( BitConverter.Is LittleEndian)
{
mSLittleEndian = myArr[0] | (myArr[1] << 8) | (myArr[2] << 16) | (myArr[3]
<< 24);
}
}
s5 = Environment.Tic kCount;
s1 = s2-s1;
s2 = s3-s2;
s3 = s4-s3;
s4 = s5-s4;
Console.WriteLi ne("Time 1: {0} Time 2: {1} Time 3: {2} Time 4:
{3}",s1.ToStrin g(),s2.ToString (),s3.ToString( ),s4.ToString() );

[Jeffrey Tan[MSFT]]

Hi Docschnipp,

Thanks for your feedback!

Yes, I see your concern, BSWAP instruction should be faster than manually
change the byte order. However, based on my experience, C# does not
contains the code statement to generate this specific instruction.(I think
JIT compiler takes control of the instructions generated)

To workaround this issue, I think you may use C/C++ to write a dll which
internally uses inline ASM to call BSWAP instruction. Then in C# code, you
may p/invoke the exported function of the C/C++ dll to call BSWAP
indirectly. You can also declare the C/C++ function as naked to eliminate
the function prolog and epilog.

Hope this helps!

Best regards,
Jeffrey Tan
Microsoft Online Community Support
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