Efficient I/O for 24-bit integer?

[reiner]

Hello,

perhaps someone on the list has a good idea for this. I am in need for an 
efficient method to read and write large arrays of 24-bit signed integer values 
to and from binary files. I have come up with the following:

read:
[sig, cnt] = fread(fid, [3, siz], 'uchar');
sig0 = sig(1,:) + 256*sig(2,:) +  65536*sig(3,:);
index = find(sig0 > 8388608);
sig0(index) = sig0(index)-16777216;
sig = sig0/8388608;


write:
sig0 = sig*8388608;
index = find(sig0 < 0);
sig0(index) = 16777216+sig0(index);
s3=floor(sig0./65536);
r=rem(sig0,66536);
s2=floor(r./256);
s1=rem(r,256);
sig=[s1 s2 s3];
fwrite(fid, sig', 'uchar');

Can this be done more efficiently? The files I read contain rather large arrays 
and I would like it to work faster.

Thanks for any ideas you might have.

Reiner Suikat



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