Comments on: Convert Binary to Base64 String

By: Grant

Grant — Sat, 05 Jun 2010 22:39:36 +0000

John's method will be faster and let someone define arbitrary mappings. Unfortunately, you can't beat .NET's implementation since its written in C++ and is unsafe code. You can use .NET Reflector to look at the Convert.ToBase64String method yourself. Microsoft can get away with that because .NET assemblies are fully trusted. When you think about it, C++ has some great and totally unsafe ways of doing this conversion.

On the whole though, unless you are converting huge amounts of these things (maybe to mime encode a big binary) you don't need a lot of speed.

Thanks for this code, it gives me a head start on my own implementation.

By: John Catfish

John Catfish — Thu, 13 May 2010 15:56:29 +0000

I almost forgot, It could also fit into the system cache!

By: John Catfish

John Catfish — Thu, 13 May 2010 15:53:00 +0000

I think you could replace the method
"static private char SixBitToChar( byte b )"
for an array.

It should be faster. It has no method call overhead, no ifs, no calculations, it is readonly and it only implies an access operation [].

string Dict = "ABCDE….abc…etc"

So instead of SixBitToChar(b)
you should do Dict[b]

By: Damian

Damian — Tue, 25 Aug 2009 08:48:23 +0000

Hi – This is a gret post that I have found extremely helpful.

I am using Base 64 to create shorter URLs as described, and I'm not too familiar with all the maths of bytes and bases.

Public Shared Function encUC(ByVal uniqueCode As String) As String

Dim val As Int64 = Convert.ToInt64(uniqueCode)
Dim retVal As String

Dim tinyByte() = System.BitConverter.GetBytes(val)

'NB THIS WILL WORK FOR A MAX OF 12 DIGIT CODES
'ReDim Preserve tinyByte(4)

Dim tinyCode = Base64.Base64Encoder.ToBase64(tinyByte)

retVal = Replace(tinyCode, "=", "_")
retVal = Replace(retVal, "/", "-")
retVal = Replace(retVal, "+", "|")

Return retVal

End Function

When I encode it seems to not give me the least possible characters in the base64 string

1000001728 encodes as wNCaOwAAAAA_

So i have shortened the byte array :
ReDim Preserve tinyByte(4)

Which is fine as my codes are a max of 12 digits, but not very elegant.

Can you suggest anything?

ALSO

When I decode a 32 bit integer (8 digit code)

Public Shared Function decUC(ByVal encCode As String) As String

Dim repCode As String = encCode
repCode = Replace(repCode, "_", "=")
repCode = Replace(repCode, "-", "/")
repCode = Replace(repCode, "|", "+")

Dim origByte(7) As Byte
origByte = Base64.Base64Encoder.FromBase64(repCode)
ReDim Preserve origByte(7)

Return System.BitConverter.ToInt64(origByte, 0)

End Function

if I don't use ReDim Preserve origByte(7) it gives me an exception on the

Return System.BitConverter.ToInt64(origByte, 0) (array to short)

As I won't always know if i'm getting an 8 or 12 digital code – I want my functions to cater for both. Any ideas?

My thanks again for a really great post that ended hours of midnight hunting