This is not my code, but a conversion from an MT5 code here

There were requests for this to be converted to MT4.

The formulae used are:

Resistance 3 = High + 2*(Pivot - Low)
Resistance 2 = Pivot + (R1 - S1)
Resistance 1 = 2 * Pivot - Low
Pivot Point = ( High + Close + Low )/3
Support 1 = 2 * Pivot - High
Support 2 = Pivot - (R1 - S1)
Support 3 = Low - 2*(High - Pivot)