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
The reason that function does not come in the OSL Language Specification, it because 'noise_turbulence' is in fact a function done in OSL, and not hard coded into the OSL source.

It's located in the 'node_texture.h' (along with the voronoi function), and it can be found in the \blender\2.XX\scripts\addons\cycles\shader\ folder.