Reading structured bit24 file data with skip

Ok here is the gist of the problem:

File structure is a big Endian machine format with an array of 1600 numbers (matrix 100X16) stored as 24bit signed integers. After each block of 1600 values, a three character word is written and the pattern then repeats:

|1600 24bit words|XXX|1600 24bit words|XXX|...

I am attempting to read all of the data into a variable using this syntax:

d=fread(fid,[100,32],'1600*bit24=>int32',24);%read in blocks of 1600 values then 24 bit skip (8bits * 3 Characters)

This produces an (unexpectedly) sized data array "d" of 100X41 elements... What am I missing here? d should be 100X32?? further the data is "jumbled up" in the variable d.

The only way I am able to correctly read this file data is:

fseek(fid,0,'bof');%skip to start of file 
%loop
d=fread(fid,[100,16],'bit24'); %read in block of 1600 data points
fseek(fid,3,'cof');%skip over 3 bytes of characters and
%repeat from loop...concatenating d with another variable to contain all data (D=[D;d]) for example

This method is S L O W but works. Why doesnt the 'skip' form of fread work correctly?

Any Help is appreciated!

[dpb]

Looks like should, granted. I'd suggest sending a small file that demonstrates the problem to official TMW support at www.mathworks.com

To speedup the workaround, preallocate D to a suitable size and populate it in the loop instead of using dynamic reallocation by concatenation as you're showing, ie, sotoo--

...
D=zeros(100,32,'int32');
while ~feof(fid)
  D(i,:)=fread(fid,[100,16],'bit24');
  i=i+1;
  ...

ADDENDUM

Have you tried memmapfile? I'm not positive it has the flexibility for the 24bit/3byte fields or not, but you might check...

Note: On looking, memmapfile doesn't have the bitN datatype, unfortunately, so it's of no help...