How to sum one field in internal table

Hi experts ,

I am passing intermal table from program to smartforms .

but i want to calculate the Quantatiy(mseg-menge) base on the material nu (MSEG-MATNR) .

am display at end of page . if data into internal table have

matnr menge unit

mat1 30 PC

mat1 40 PC

mat2 10 Kg

mat2 30. Kg

in my smartform out put display at last .

Total

Mat1 : 70 PC

Mat2 : 40 kg

Please if any body have input , you are welcome for solve this issue.

Regards

Ajay Pandey