Skip to main content

Loop Unrolling or Loop unwinding in C

What is Loop Unrolling or Loop unwinding in C?
Loop unwinding, also known as loop unrolling, is a loop transformation technique that attempts optimize a program's execution speed at the expense of its size.
The goal of loop unwinding is to increase the program's speed by reducing (or eliminating) the "end of loop" test on each iteration. Loops can be re-written as a sequence of independent statements which eliminates the loop controller overhead.
The major side effects of loop unrolling is The increased register usage in a single iteration to store temporary variables (though much will depend on possible optimizations), which may hurt performance.
The code size expansion after the unrolling, which is undesirable for embedded applications and for purposes of code readability. Large code can also cause an increase in instruction cache misses, which may adversely affect performance.
A simple example
A procedure in a computer program is to delete 100 items from a collection. This is accomplished by means of a for-loop which calls the function delete(item_number):


for (int x = 0; x <>



If this part of the program is to be optimized, and the overhead of the loop requires significant resources compared to that for delete(x), loop unwinding can be used to speed it up. This will result in an optimized code fragment like:


for (int x = 0; x <>


As a result of this modification, the new program has to make only twenty loops, instead of a hundred.

check example here.

Comments

Popular posts from this blog

www.meficai.org ICAI MEF 2008-09 Acknowledgement

www.meficai.org ICAI MEF 2008-09 Acknowledgement Institute of Chartered Accountants of India- ICAI Click here to download your acknowledgement or direct link http://www.meficai.org/mymefstatus.jsp Multipurpose Empanelment Form (MEF) 2008-09 Download Multipurpose Empanelment Form (MEF) for the year 2008-09 meficai, www.meficai.org, mef icai, bessel function, dhaka stock exchange ICAI-Multipurpose Empanelment Form (MEF) 2008-09-MEFICAI. [Last date for submission of applications on the website: 15th September, 2008. Last date for receipt of hard copy of duly signed declaration: 25th September, 2008]

ahsec results 2008 | www.ahsec.nic.in

The official website of assam higher secondary education council Results of Assam is down seems they are uploading results , direct link to check ahsec results 2008 is http://resultsassam.nic.in/index.asp You can find results of AHSEC at the link above. current page The Website www.ahsec.nic.in Designed Developed & Hosted by NIC, Assam State Centre, Guwahati is down for result uploading. keep checking this page, I will update as soon as news comes. All the best to AHSEC - assam higher secondary education council students. Direct links http://assam.nic.in/ www.ahsec.nic.in http://resultsassam.nic.in/

Rajasthan Board 10th Results | rajedubord.nic.in | RBSE

Raj Board of Secondary Education, Rajasthan Results at rajeduboard.nic.in Board of Secondary Education, Rajasthan Ajmer declared result of secondary examination today at 4PM official site is rajedubord.nic.in check Secondary Examination- 2008 Result (To be announced on July 1st, 2008 at 4:00 PM) source http:// rajresults.nic.in / Declared result Praveshika Examination-2008 Result (Announced on June 25, 2008 at 4:00 PM) The history of the Board of Secondary Education Rajasthan (BSER) is a remarkable panorama of progressive record of the futurological vision for developing a dynamic system of various sub-systems of examinations and highlights of the academic excellence of the last four decades. The BSER took rapid strides for promotion and development of Secondary Education in Rajasthan, spread over 3,42,239 sq. km. and in more than 6000 schools located in 32 districts involving 8.5 lakhs students for Secondary and Senior Secondary Examination in the year 2000. At present the Board is