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From: roger &lt;northsolomonsea@gmail.com&gt;
Newsgroups: comp.soft-sys.matlab
Subject: matlab typecast function very slow
Date: Tue, 3 Nov 2009 03:30:46 -0800 (PST)
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Hi,

I have a function that reads large binary files by reading a couple of
numbers per time in a complicated loop using fread.

Since the function isn't too fast I thought I'd read the entire file
at once as uint8 and then typecast byte by byte to the relevant
datatypes.

To my surprise the typecast method is actually a _lot_ slower than
consecutively using fread, on inspection the profiler shows that the
typecast function is the main culprit.

The function that serves the typecast.m function is a mex file called
typecastc.mexw32 (on my 32 bit system that is). It seems to be a
function which is compiled from an accompying c file that is located
in the same private directory: typecastc.c

When I look at the c source file I see that the function itself
doesn't do any typecasting, it just creates a relevant datatype with
the mex mxCreateNumericMatrix and then leaves the actual typecasting
to the mx libraries.

So all in all the typecasting slowness seems a result of matlab's
inability to deal with c-style pointers from m-files and the penalty
for this is the mx library overhead.

An odd situation.

Anyone have a better method (than the mathworks have ;) for reading/
typecasting?

best regards R
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