In reply to svishnu:
In 2002 I wrote the book Real Chip Design and Verification Using Verilog and VHDL, and in that book I address the general topic of doing arithmetic in Verilog and VHDL.
The following is an extraction of pages from that book that provides an explanation of those concepts with lots of examples.
The code examples referenced in the book are at:
http://systemverilog.us/vf/arith_verilog.zip
Hopefully, that will provide answers for you as your question really involved your thorough understanding of how arithmetic is handled in Verilog (and SystemVerilog), including the automatic extension of bits for unmatched sized operands.
Ben Cohen
http://www.systemverilog.us/ ben@systemverilog.us
- SVA Handbook 4th Edition, 2016 ISBN 978-1518681448
- A Pragmatic Approach to VMM Adoption 2006 ISBN 0-9705394-9-5
- Using PSL/SUGAR for Formal and Dynamic Verification 2nd Edition, 2004, ISBN 0-9705394-6-0
- Real Chip Design and Verification Using Verilog and VHDL, 2002 isbn 978-1539769712
- Component Design by Example ", 2001 ISBN 0-9705394-0-1
- VHDL Coding Styles and Methodologies, 2nd Edition, 1999 ISBN 0-7923-8474-1
- VHDL Answers to Frequently Asked Questions, 2nd Edition ISBN 0-7923-8115