baseConvert() & 32-bit ops (was Best array population & access optimization)

[Dar Scott]

On Saturday, June 21, 2003, at 03:12 PM, Graham wrote:

> Not wanting to stop the flow, but for the benefit of the rest of us, 
> what is this topic actually about? I didn't realise that a discussion 
> in this list could go entirely over my head... I feel really stupid.

Mostly about primitives that those writing encryption software would be 
interested in.  (There are more general uses.)  In particular, Mark is 
working with Blowfish that uses 32-bit half blocks.

Even thought Revolution is 8-byte (double) floating point in its 
arithmetic, this is suitable for representing an (imaginary, perhaps) 
32-bit number.  There are some built-in Transcript functions that work 
with this 32-bit view.

These include bitAnd, bitOr, bitNot and bitXor.  These perform bit-wise 
logical operations on numbers.

The baseConvert() uses a 32-bit number as an intermediate value, it 
seems.

Missing are the shift and rotate commands/functions.  Fortunately, Mark 
doesn't really need those.  Those can easily be written, but they will 
be slow.

Also important is initialization, traditionally from hex tables.  This 
can be done with baseConvert, binaryEncode and binaryDecode.

Another common task is the mapping of strings to and from the block 
list/array used by some algorithms.  I think binaryEncode and 
binaryDecode are helpful here.

Other Revolution commands/functions such as compress and md5Digest are 
also handy.  I wouldn't use the built-in random for this.  I don't 
think Mark needs random for what he wants.

Algorithms often use arrays or matrices called boxes in this jargon.  
In Blowfish, mark is looking at ways to represent those.  He might 
represent all S -boxes and P-boxes as a single array (handy as a single 
unit), or he might break the S-boxes into 4 arrays and use a separate 
18 variables for the P boxes (great for speed).  That is part of the 
problem in optimization and maximizing utility.

These same problems also come up in other areas such as control I/O and 
reading & writing some kinds of binary files.

Dar Scott