__intSum:
First Argument – The First integer value/Jmeter Variable Second Argument – The Second integer Value/Jmeter Variable . . . Nth Argument – The Nth integer value/Jmeter Variable Last Argument – A variable or a reference name which will store the value for the addition and can be reused later.
If User wants to increment a counter value by 2 with each iteration. {__intSum(${tj_counter},2,tj_counter)} Explanation: 1)__intSum function name 2)${tj_counter} First argument 3)1 Second Argument 4)tj_counter Last Argument is the Reference name where the addition value get stored.
1)Is the function __counter better than __intSum? ANS Yes Of course. Even __intSum can be used to increment a number with each thread which is quite similar to __counter function. But __counter function starts the counter with 1 and increment it by 1 and with __intSum we can start it from any number and increment it by any value. 2)Is there any scenario we can think of? Yeah. It will be helpful while user input needs any addition of any numbers. In that case we can simply add two or multiple values and use the variable to reference it any filed we want to. 
__longSum:
First Argument – The First long value Second Argument – The Second long Value . . . Nth Argument – The Nth long value Last Argument – A variable or a reference name which will store the value for the addition and can be reused later.
If User wants to increment a certain value by a certain number(Say to match the session ID with each iteration.) __longSum(${tj_sessionid},65345,tj_sessionid)} Explanation: 1)__longSum Function Name 2)${tj_sessionid} First argument 3)65345 Second Argument 4)tj_sessionid Last Argument is the variable name where the addition value get stored and can be reused later.
