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which referencing newlibs version of single precision float round. How to round off a floatig point value to two places. It may cause a slight performance hit, however, and will likely have issues with rounding certain known "problem" floating-point values such as 0.49999999999999994 or similar values.Alternatively, if you have access to a C++11-compliant compiler, you could just grab std::round() from its Based on Kalaxy's response, the following is a templated solution that rounds any floating point number to the nearest integer type based on natural rounding.

The conversion truncates; that is, the fractional part If there is something missing in my explanation please let me know.Nice complete answer - especially the just below 0.5 part. Type cast the result to int and return. @stijn It is ok for all values, if you do not care in which direction the values exactly in-between two integers are rounded. If decimal value is from ”.1 to.5″, it returns integer value less than the argument. By using our site, you acknowledge that you have read and understand our 3. For some values, such as 0.49999997f or the equivalent double, the answer is just wrong - it will be rounded to 1.0 when all agree that it should be zero. n=3.So,It might be an inefficient dirty way of conversion but heck, it works lol. I also exhaustively tested the single-precision case.It's good to make the distinction between different versions of 'round'.

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I'm not sure that rounding -1.5 to -1.0 is standard though, I would expect -2.0 by symetry. You are asking for round to closest integer.Rounding conversions mean rounding ± float/double to nearest floor/ceil float/double. This question was asked and answered in another time when life was hard and the joys were few. For example, 5.567 should become 5.57 and 5.534 should become 5.53Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.Attention reader! You can write one yourself though. I observed the most compact code on GPUs, where I use the following implementation of round in asm for x86 architecture and MS VS specific C++:Best way to rounding off a floating value by "n" decimal places, is as following with in O(1) time:-We have to round off the value by 3 places i.e. But then the question becomes: which rounding function do you pick?There are two math library rounding functions that use the current default rounding mode: In FP code, it's usually a big win to inline small functions. @PeterCordes Modern optimizations are welcome. Therefore the IEEE floating point standards cannot possibly be represented perfectly as decimal numbers for all binary digital representations.This is not an issue with the rounding algorithms.

I've never thought that even rounding is a non-trivial operation.Does not give the expected result for 0.49999999999999994 though (well, depending on what you expect of course, but 0 seems more reasonable to me than 1)@stijn Good catch. 2.

Else subtract 0.5. @ truthseeker: Yeah, I had to see the required type of return value. The following basic command produces neither errors nor warnings with g++ 6.3.1, x86_64-w64-mingw32-g++ 6.3.0, clang-x86_64++ 3.8.0, and Visual C++ 2015 Community.When dividing two ordinal numbers, where T is short, int, long, or another ordinal, the rounding expression is this.There is no doubt that odd looking inaccuracies appear in floating point operations, but this is only when the numbers appear, and has little to do with rounding.The source is not just the number of significant digits in the mantissa of the IEEE representation of a floating point number, it is related to our decimal thinking as humans.Ten is the product of five and two, and 5 and 2 are relatively prime.

@Shafik this is a great answer. Featured on Meta By using our site, you
It seems unlikely that anyone without intimate knowledge of floating point implementations could correctly implement this function: edit close. ?There's no round() in the C++98 standard library.

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For example, 5.567 should become 5.57 and 5.534 should become 5.53.

If num is positive then add 0.5.

Remember, when rounding a binary (as opposed to System.Decimal) floating-point type to a number of decimals greater than 0, that typically the "midpoint" is not exactly representable. The above is one common way but there are others such as The C++03 standard relies on the C90 standard for what the standard calls the The library described in clause 7 of ISO/IEC 9899:1990 and clause 7 of