CODEWITHSUNDEEP
matlabfloating-point
Veridian
Veridian

Reputation: 3667

How to turn off denormal number support in MATLAB?

I am trying to turn off denormal number support in matlab, so that basically any two computations that would result in a denormal number would instead just result in zero (DAZ, FTZ)

I've researched several sites include the one below, but I haven't found anything about doing this.

http://blogs.mathworks.com/cleve/2014/07/21/floating-point-denormals-insignificant-but-controversial-2/

Upvotes: 3

Views: 446

Answers (1)

horchler
horchler

Reputation: 18484

I've never heard of such an option in Matlab. It would likely require deep manipulation of a lot of the floating-point math, effectively requiring a new datatype to be supported if this were to be an easily toggle-able option in Matlab. You could write your own mex C code to do this (more here and here) for an individual function.

And of course you can get something like this with one line of Matlab – here's an example:

a = [1e-300 1e-310 1e-310];
b = [1e-301 1e-311 1e-310];
x = a-b;
x(abs(x(:)) < realmin(class(x))) = 0;

where realmin is the smallest normalized floating-point number. However, the floating point math is still performed using the extended denormal/subnormal values in a. It's just the output that's clipped to zero.

Unless you're doing this for fun an experimentation, or possibly running code on an embedded platform, I'd really recommend against disabling denormals as a form of optimization. Instead, focus on why your values are so small and how you might rescale your problem to avoid the issue entirely.

Upvotes: 0

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