# OSL noise_turbulence function

I found that people use noise_turbulence function in noise writing. Also i noticed that it was used in wave texture node implementation using osl here:https://svn.blender.org/svnroot/bf-blender/trunk/blender/intern/cycles/kernel/shaders/node_wave_texture.osl

But there's no any function like that in OSL-Languagespec. So how to write something similar?

Thank you