HRA mentioned on the salary slip in the EARNINGS section is the one
HRA provided by company.
The amount of HRA that you can claim as tax exemption (which is calculated as per the three rules that you have written) is different and may or may not be mentioned in your salary slip.
If you want to know the following:
1. Amount of tax exemption that you can get with the HRA mentioned in your salary slip AND
2. How much rent can get you maximum tax exemption
Then you can find it using this calculator:
http://am22tech.com/s/22...Tax-Exemption-India.aspx