Institute for Information Resources is the one who maintains and gives Global Impact Factor to journals.  

The Global impact factor is calculated per year on the basis of a 100 points contribution scale and on  Number of articles published during a year. Articles are selected from each issue and their quality is judged.

Evaluation Methodology

The below quality factors are evaluated:

Originality Contribution (OC): 50%

Scientific Quality Contribution(SQC):20%

Review Process Contribution (RPC):20%

Regularity and stability Contribution(RSC):5%

Technical Editing Quality Contribution(TEQC):5%

Total Quality Contributing Factor (TQCF) OC+SQC+RPC+RSC+TEQC

Thank you sir for your kind response about GIF, Can you tell us where is Institute for Information Resources? Has this GIF database recommendation from any scientific society or government, because now majority of the journals are taking indexing of GIF and there IF are higher than as compare to World top class databases Journals. I got this anwser from wikipedia...........

https://en.wikipedia.org/wiki/Impact_factor

There are many Quality rating calculation agencies in the world, like Thomson Reuters, Scopus, Gif , Index copernicus etc.. They all have their own different methods and criteria. 

Well, I found this:

"The story of fake impact factor companies and how we detected them" who claim that " Universal Impact Factor (UIF), Global Impact Factor (GIF), and Citefactor, [are fake] and there even is a fake Thomson Reuters Company "

Read it here: Article The story of fake impact factor companies and how we detected them

Thomson Reuters is not fake but doesn't exist at present. It is Web of Science (former Web of Knowledge)

Good Q