{"id":2243,"date":"2011-09-26T09:28:12","date_gmt":"2011-09-26T08:28:12","guid":{"rendered":"https:\/\/blogs.mentor.com\/colinwalls\/?p=2243"},"modified":"2026-03-26T16:35:53","modified_gmt":"2026-03-26T20:35:53","slug":"efficient-code-a-quiz","status":"publish","type":"post","link":"https:\/\/blogs.sw.siemens.com\/embedded-software\/2011\/09\/26\/efficient-code-a-quiz\/","title":{"rendered":"Efficient code – a quiz"},"content":{"rendered":"

I was recently reading a set of “golden rules” for embedded programming. I am very skeptical about such proscriptive instructions as, for them to be valid, a great many assumptions must be made and clearly stated. These rules were supposed to promote the production of safe, efficient code. I am OK with “safe” – that simply means that the code does what it is supposed to do, without deviation as a result of unexpected data or unexpected side-effects. I am not so sure about “efficient”, as that depends entirely on the design parameters in force; it might mean fast or it might mean small, for example. And what about maintainability and portability being significant parameters?<\/p>\n

So, instead of trying to outline rules myself, I thought that I might set out to find out what real developers think …<\/p>\n

Just for fun [budgets to not stretch to offering a prize], I would like to pose a question and request answers by comment or email<\/a>:<\/p>\n

You are developing a system, where execution speed is important. At one point in the code, there is an unsigned integer variable x which needs to be divided by 8. I can immediately think of 4 ways to code this:<\/p>\n

x \/= 8;<\/pre>\n
x = x \/ 8;<\/pre>\n
x >>= 3;<\/pre>\n
x = x >> 3;<\/pre>\n
My question is: which of these options is the most efficient and why? Of course, if you have other suggestions about how to address the problem, I would be very interested to hear.<\/p>\n
I will publish some results and my answer in a couple of weeks.<\/p>\n","protected":false},"excerpt":{"rendered":"
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