% index_to_binary.m
% Takes a list of index values and converts them to [length, value] lists.
% usage:
%	index = bitstring_to_index( [0 0 0 0 1] );
%	[bitlength, value] = index_to_binary(index)
% returns
%	length = 5
%	value = 1
%
% index_to_binary() and binary_to_index() convert
% back and forth freely, like
% bitstring_to_index() and index_to_bitstring(). For example,
%	[bitlength, value] = index_to_binary( 1:10 );
%	index = binary_to_index( bit_length, value )
% returns
%	index = [ 1 2 3 4 5 6 7 8 9 10 ]
% 
% See also BINARY_TO_INDEX,
% INDEX_TO_BITSTRING, PRINT_BITSTRINGS, BITSTRING_TO_INDEX.

% Change log:
% 1999-06-30:DAV: David Cary <d.cary@ieee.org> started.

function [length,value] = index_to_binary(index)

% IEEE754 double precision can handle integers exactly
% up to (but not including) 2^53+1. See BITMAX.
if( 2^53 < max(index(:)) )
   error('Sorry, this is too big for me to handle.')
end;

[dummy, lengthp1] = log2( index+1 );
length = lengthp1 - 1;
value = (index - 2.^length) + 1; % must be done in this order to do 2^53 correctly.

% end index_to_binary.m