Where to find it:

NodeGraph / Right Mouse Click / Add Nodes / Math / Extension Pack / L /

log2 returns the base 2 logarithm of x, i.e. the value y which satisfies x=2^y

https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/log2.xhtml

•X

Specify the value of which to take the base 2 logarithm

•Output RGB

Separate computation for Input Channels Red, Green, Blue with an Alpha Channel of 1.0

•R

Computation for Input Red channel only, saved into R, G and B channel with an Alpha of 1.0

•G

Computation for Input Green channel only, saved into R, G and B channel with an Alpha of 1.0

•B

Computation for Input Blue channel only, saved into R, G and B channel with an Alpha of 1.0

•A

Computation for Input Alpha channel only, saved into R, G and B channel with an Alpha of 1.0