so, is it legal to use source code from papers and such:

like this paper on perlin noise: [url]http://mrl.nyu.edu/~perlin/paper445.pdf[/url] links to this source code: [url]http://mrl.nyu.edu/~perlin/noise/[/url]

and stam's famous talk on fluid dynamics, includes source code throughout, annotated with instructions like "add these macros to the beginning of your code" [url]http://www.dgp.toronto.edu/people/stam/reality/Research/pdf/GDC03.pdf[/url]

I'm just not sure if it's legal to copy and paste this to use in your own commercial code. if I were to make my own implementation, it would end up being close to identical, since I'd probably use the source code as a reference. I know very little about copyright law, including how it applies in these situations, and I can never find usage and licensing terms for these. Nor did googling any terms I could think of provide me the specific answer I need.

does anyone know for sure what the rules/laws are here, or where I can find the answer?