These files contain noise functions that are compatible with all
current versions of GLSL (1.20 and up), and all you need to use them
is provided in the source file. There is no external data, and no
setup procedure. Just cut and paste and call the function.

GLSL has a very rudimentary linker, so some helper functions are
included in several of the files with the same name. If you want to
use more than one of these functions in the same shader, you may run
into problems with redefinition of the functions mod289() and permute().
If that happens, just delete any superfluous definitions.

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Source: https://github.com/ashima/webgl-noise
Changes:
 - 10 April 2018, Unity Technologies, Ported to HPC#