sharadsinha

Posts Tagged ‘Big addition’

Relearning addition

In Design Methodologies, Education, Embedded Systems, Mathematics on March 22, 2013 at 7:13 PM

Alvin Toffler in his book “Future Shock” says that  “The illiterate of the 21st century will not be those who cannot read or write; they will be those who cannot learn, unlearn, and relearn“. Taking this quote a little out of context in which Alvin used it, I would say that the process of learning, unlearning and relearning basically embodies the principles of evolution and adaptation. And these are equally applicable to education. Are these emphasized enough in universities and schools? Can they be taught? May be yes, may be no. I will give one simple example here. Every electronics or computer engineer would have done some basic C programming. To add two numbers, A and B, one just needs to use the expression ‘A+B’. Does it always work? Not in the world of computers where one has to deal with overflows and underflows. And there is always a limit to the biggest number that a computer or a computing platform can support.

So, how are we going to add two arbitrarily sized positive integers. Examples of positive integers are 123456, 90913456 etc. I will use positive integers to illustrate ‘learn, unlearn and relearn’. The example can easily be extended to other data types. In C language, the integer data type can only support a maximum value of 2,147,483,647 when adding two numbers. So there is an overflow if sum exceeds this value and addition is not possible if either A or B is bigger than this value. To avoid this, one can use other data types supporting greater number of bits until one hits yet another ceiling. After a point, you hit the final ceiling. If the numbers are really so big, one way to deal with them is to go back to our old school days when we learned to add numbers: 2 digits at a time with a carry propagated. Yes, that is all you need to do! And this does not require in-depth of knowledge of various IEEE methods to represent numbers. It is simple and good old school method. Of course, the old school method may not have a very wide application, but it does help where possible and makes it clear that  the symbol for addition “+” (or the add operator as it is referred to in programming languages) should not make us forget how addition is done. We “learn” to add 2 digits at a time in school, then we learn to use the “+” operator in programming languages. Thereafter we have to unlearn this concept to relearn (or recall) the school method.  I have written a reference implementation in C which you can find here. You can also find its link under the software tools tab here.

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