verify_nii_ext(ext)

%  Verify NIFTI header extension to make sure that each extension section
%  must be an integer multiple of 16 byte long that includes the first 8
%  bytes of esize and ecode. If the length of extension section is not the
%  above mentioned case, edata should be padded with all 0.
%
%  Usage: [ext, esize_total] = verify_nii_ext(ext)
%
%  ext - Structure of NIFTI header extension, which includes num_ext,
%       and all the extended header sections in the header extension.
%       Each extended header section will have its esize, ecode, and
%       edata, where edata can be plain text, xml, or any raw data
%       that was saved in the extended header section.
%
%  esize_total - Sum of all esize variable in all header sections.
%
%  NIFTI data format can be found on: http://nifti.nimh.nih.gov
%
%  - Jimmy Shen ([e-mail])
%
function [ext, esize_total] = verify_nii_ext(ext)

   if ~isfield(ext, 'section')
      error('Incorrect NIFTI header extension structure.');
   elseif ~isfield(ext, 'num_ext')
      ext.num_ext = length(ext.section);
   elseif ~isfield(ext, 'extension')
      ext.extension = [1 0 0 0];
   end

   esize_total = 0;

   for i=1:ext.num_ext
      if ~isfield(ext.section(i), 'ecode') | ~isfield(ext.section(i), 'edata')
         error('Incorrect NIFTI header extension structure.');
      end

      ext.section(i).esize = ceil((length(ext.section(i).edata)+8)/16)*16;
      ext.section(i).edata = ...
	[ext.section(i).edata ...
	 zeros(1,ext.section(i).esize-length(ext.section(i).edata)-8)];
      esize_total = esize_total + ext.section(i).esize;
   end

   return                                       % verify_nii_ext